Process for producing ethanol using a stacked bed reactor

ABSTRACT

The present invention produces ethanol in a stacked bed reactor that comprises a first catalyst comprising platinum and tin and a second catalyst comprising copper or an oxide thereof. The crude ethanol product may be separated and ethanol recovered.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.13/094,714, filed Apr. 26, 2011, and a continuation-in-part of U.S.application Ser. No. 13/178,659, filed Jul. 8, 2011, both of whichclaims priority to U.S. Provisional App. No. 61/363,056, filed on Jul.9, 2010, the entirety of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to processes for producingalcohol and, in particular, to forming an ethanol composition using astacked bed reactor comprising a first catalyst comprising platinum andtin and a second catalyst comprising copper or an oxide thereof. In someembodiments, the second catalyst may further comprise zinc, aluminum,cobalt, or oxides thereof.

BACKGROUND OF THE INVENTION

Ethanol for industrial use is conventionally produced from organic feedstocks, such as petroleum oil, natural gas, or coal, from feed stockintermediates, such as syngas, or from starchy materials or cellulosematerials, such as corn or sugar cane. Conventional methods forproducing ethanol from organic feed stocks, as well as from cellulosematerials, include the acid-catalyzed hydration of ethylene, methanolhomologation, direct alcohol synthesis, and Fischer-Tropsch synthesis.Instability in organic feed stock prices contributes to fluctuations inthe cost of conventionally produced ethanol, making the need foralternative sources of ethanol production all the greater when feedstock prices rise. Starchy materials, as well as cellulose materials,are converted to ethanol by fermentation. However, fermentation istypically used for consumer production of ethanol, which is suitable forfuels or human consumption. In addition, fermentation of starchy orcellulose materials competes with food sources and places restraints onthe amount of ethanol that can be produced for industrial use.

Ethanol production via the reduction of alkanoic acids and/or othercarbonyl group-containing compounds, including esters, has been widelystudied, and a variety of combinations of catalysts, supports, andoperating conditions have been mentioned in the literature.

More recently, even though it may not still be commercially viable ithas been reported that ethanol can be produced from hydrogenating aceticacid using a cobalt catalyst at superatmospheric pressures such as about40 to 120 bar, as described in U.S. Pat. No. 4,517,391.

On the other hand, U.S. Pat. No. 5,149,680 describes a process for thecatalytic hydrogenation of carboxylic acids and their anhydrides toalcohols and/or esters utilizing a platinum group metal alloy catalyst.The catalyst is comprised of an alloy of at least one noble metal ofGroup VIII of the Periodic Table and at least one metal capable ofalloying with the Group VIII noble metal, admixed with a componentcomprising at least one of the metals rhenium, tungsten or molybdenum.Although it has been claimed therein that improved selectivity to amixture of alcohol and its ester with the unreacted carboxylic acid isachieved over the prior art references it was still reported that 3 to 9percent of alkanes, such as methane and ethane are formed as by-productsduring the hydrogenation of acetic acid to ethanol under their optimalcatalyst conditions.

A slightly modified process for the preparation of ethyl acetate byhydrogenating acetic acid has been reported in EP0372847. In thisprocess, a carboxylic acid ester, such as for example, ethyl acetate isproduced at a selectivity of greater than 50% while producing thecorresponding alcohol at a selectivity less than 10% from a carboxylicacid or anhydride thereof by reacting the acid or anhydride withhydrogen at elevated temperature in the presence of a catalystcomposition comprising as a first component at least one of Group VIIInoble metal and a second component comprising at least one ofmolybdenum, tungsten and rhenium and a third component comprising anoxide of a Group IVB element. However, even the optimal conditionsreported therein result in significant amounts of by-products includingmethane, ethane, acetaldehyde and acetone in addition to ethanol. Inaddition, the conversion of acetic acid is generally low and is in therange of about 5 to 40% except for a few cases in which the conversionreached as high as 80%.

Copper-iron catalysts for hydrogenolyzing esters to alcohols aredescribed in U.S. Pat. No. 5,198,592. A hydrogenolysis catalystcomprising nickel, tin, germanium and/or lead is described in U.S. Pat.No. 4,628,130. A rhodium hydrogenolysis catalyst that also contains tin,germanium and/or lead is described in U.S. Pat. No. 4,456,775.

Several processes that produce ethanol from acetates, including methylacetate and ethyl acetate, are known in the literature.

WO8303409 describes producing ethanol by carbonylation of methanol byreaction with carbon monoxide in the presence of a carbonylationcatalyst to form acetic acid which is then converted to an acetate esterfollowed by hydrogenolysis of the acetate ester formed to give ethanolor a mixture of ethanol and another alcohol which can be separated bydistillation. Preferably the other alcohol or part of the ethanolrecovered from the hydrogenolysis step is recycled for furtheresterification. Carbonylation can be effected using a CO/H₂ mixture andhydrogenolysis can similarly be conducted in the presence of carbonmonoxide, leading to the possibility of circulating gas between thecarbonylation and hydrogenolysis zones with synthesis gas, preferably a2:1 H₂:CO molar mixture being used as makeup gas.

WO2009063174 describes a continuous process for the production ofethanol from a carbonaceous feedstock. The carbonaceous feedstock isfirst converted to synthesis gas which is then converted to ethanoicacid, which is then esterified and hydrogenated to produce ethanol.

WO2009009320 describes an indirect route for producing ethanol.Carbohydrates are fermented under homoacidogenic conditions to formacetic acid. The acetic acid is esterified with a primary alcohol havingat least 4 carbon atoms and hydrogenating the ester to form ethanol.

EP2060555 describes a process for producing ethanol where a carbonaceousfeedstock is converted to synthesis gas which is converted to ethanoicacid, which is then esterified and which is then hydrogenated to produceethanol. EP2072489 and EP2186787 also describe a similar process wherethe esters produced from esterification are fed to the alcohol synthesisreactor used to produce ethanol and methanol.

US Pub. No. 20110046421 describes a process for producing ethanolcomprising converting carbonaceous feedstock to syngas and convertingthe syngas to methanol. Methanol is carbonylated to ethanoic acid, whichis then subjected to a two stage hydrogenation process. First theethanoic acid is converted to ethyl ethanoate followed by a secondaryhydrogenation to ethanol.

US Pub. No. 20100273229 describes a process for producing acetic acidintermediate from carbohydrates, such as corn, using enzymatic millingand fermentation steps. The acetic acid intermediate is acidified withcalcium carbonate and the acetic acid is esterified to produce esters.Ethanol is produced by a hydrogenolysis reaction of the ester.

U.S. Pat. No. 5,414,161 describes a process for producing ethanol by agas phase carbonylation of methanol with carbon monoxide followed by ahydrogenation. The carbonylation produces acetic acid and methylacetate, which are separated and the methyl acetate is hydrogenated toproduce ethanol in the presence of a copper-containing catalyst.

U.S. Pat. No. 4,497,967 describes a process for producing ethanol frommethanol by first esterifying the methanol with acetic acid. The methylacetate is carbonylated to produce acetic anhydride which is thenreacted with one or more aliphatic alcohols to produce acetates. Theacetates are hydrogenated to produce ethanol. The one or more aliphaticalcohols formed during hydrogenation are returned to the aceticanhydride esterification reaction.

U.S. Pat. No. 4,454,358 describes a process for producing ethanol frommethanol. Methanol is carbonylated to produce methyl acetate and aceticacid. The methyl acetate is recovered and hydrogenated to producemethanol and ethanol. Ethanol is recovered by separating themethanol/ethanol mixture. The separated methanol is returned to thecarbonylation process.

The need remains for improved processes for efficient ethanol productionby reducing esters on a commercially feasible scale.

SUMMARY OF THE INVENTION

In a first embodiment, the present invention is directed to a processfor producing ethanol comprising the steps of introducing a feed streamand hydrogen into a stacked bed reactor that comprises a first bed and asecond bed to produce a crude ethanol product, wherein the first bedcomprises a first catalyst on a first support and the second bedcomprises a second catalyst comprising copper or an oxide thereof on asecond support, and recovering ethanol from the crude ethanol product inone or more columns. In one embodiment, the first catalyst comprisesplatinum and tin on a first support. In one embodiment, the secondcatalyst preferably further comprises zinc, aluminum, cobalt, or oxidesthereof.

In a second embodiment, the present invention is directed to a processfor producing ethanol comprising the steps of introducing hydrogen and afeed stream comprising from 5 to 40 wt. % ethyl acetate and 60 to 95 wt.% acetic acid into a stacked bed reactor to produce a crude ethanolproduct. The stacked bed reactor comprises a first bed and a second bed.The first bed comprises a first catalyst comprising platinum and tin ona first support comprising a support modifier selected from the groupconsisting of WO₃, MoO₃, Fe₂O₃, Cr₂O₃, Nb₂O₅, V₂O₅, MnO₂, CuO, Co₂O₃,and Bi₂O₃, and the second bed comprises a second catalyst comprisingcopper or an oxide thereof on a second support. The process furtherinvolves recovering ethanol from the crude ethanol product in one ormore columns.

In another embodiment, the present invention is directed to a processfor producing ethanol comprising the steps of introducing hydrogen and afeed stream comprising from 5 to 40 wt. % ethyl acetate and 60 to 95 wt.% acetic acid into a stacked bed reactor to produce a crude ethanolproduct. The stacked bed reactor comprises a first bed and a second bed.The feed stream is fed to the first bed to yield a reactor streamcomprising ethyl acetate and ethanol that is fed to the second bed toyield the ethanol product.

In a third embodiment, the present invention is directed to a processfor producing ethanol comprising the steps of introducing hydrogen and afeed stream into a stacked bed reactor that comprises a first bed and asecond bed to produce a crude ethanol product, wherein the first bedcomprises a first catalyst comprising platinum and tin on a firstsupport, and the second bed comprises a second catalyst comprisingcopper or an oxide thereof on a second support, and wherein the firstsupport and second support each comprise alumina, and recovering ethanolfrom the crude ethanol product in one or more columns.

In a fourth embodiment, the present invention is directed to a processfor producing ethanol comprising the steps of introducing hydrogen and afeed stream into a stacked bed reactor that comprises a first bed and asecond bed to produce a crude ethanol product, wherein the first bed hasa bed volume that is larger than the second bed, wherein the first bedcomprises a first catalyst, and the second bed comprises a secondcatalyst that is different than the first catalyst, and recoveringethanol from the crude ethanol product in one or more columns. In oneembodiment, acetic acid conversion in the first bed is greater than 97%.A high conversion allows a low acetic acid concentration to be fed tothe second bed, preferably less than 3 wt. %. In one embodiment, the bedvolume of the first bed is at least twice as large as the second bed.

BRIEF DESCRIPTION OF DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, wherein like numeralsdesignate similar parts.

FIG. 1 is a schematic diagram of a hydrogenation process having astacked bed reactor and four columns in accordance with an embodiment ofthe present invention.

FIG. 2 is a schematic diagram of another hydrogenation process having astacked bed reactor with two columns and an intervening water removal inaccordance with an embodiment of the present invention.

FIG. 3 is a schematic diagram of yet another hydrogenation processhaving a stacked bed reactor with three columns in accordance with anembodiment of the present invention.

FIG. 4 is a schematic diagram of yet another hydrogenation processhaving a stacked bed reactor with a single column in accordance with anembodiment of the present invention.

FIG. 5 is a schematic diagram of yet another hydrogenation processhaving a stacked bed reactor with a heavy ends column in accordance withan embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates generally to processes for forming ethanolusing a stacked bed reactor. For purposes of the present invention, astacked bed reactor comprises at least two different catalysts. Eachcatalyst may be a hydrogenation catalyst capable of reducing acarboxylic acid or ester thereof to an alcohol. Preferably, the stackedbed reactor comprises two or more beds. In each additional bed there maybe an additional hydrogenation catalyst.

In one embodiment, the first bed may have a greater bed volume than theother beds, and, preferably, the bed volume of the first bed may be atleast twice as large as the other beds, and more preferably at least 2.2times larger or at least 2.3 times larger. A large bed may provide forvery high conversions of acetic acid, e.g., greater than 97%, greaterthan 98% or greater than 99%. In one embodiment reaction stream from thefirst bed contains very low concentrations of acetic acid, e.g., lessthan 3 wt. %, or less than 2 wt. % or less than 0.5 wt. %. In someembodiments, the reaction stream from the first bed may be substantiallyfree of acetic acid. Without being bound by theory, a larger first bedmay ensure that substantially all of the acetic acid is consumed andthus the amount of acetic acid fed to the second bed is reduced. Thesecond bed may comprise a copper catalyst that may become less stableand lose catalytic activity in the presence of acetic acid and/or water.Reducing the amount of acetic acid that is fed to the second bed thatcontains the copper catalyst may improve the conversion of ethyl acetateto ethanol.

A feed stream that comprises acetic acid and/or ethyl acetate may be fedto the stacked bed reactor. In one embodiment, acetic acid may beconverted in the first bed. Acetic acid may be converted to ethanoland/or ethyl acetate. In the second bed, ethyl acetate may be converted,preferably to ethanol. Preferably, ethyl acetate is converted to ethanolin the second bed in the absence of acetic acid.

A problem feeding a mixed stream of acetic acid and ethyl acetate isthat catalysts for converting acetic acid may not convert the ethylacetate in the feed. Without converting ethyl acetate, the feed to thereactor must contain very low amounts of ethyl acetate and ethyl acetatemust be purged from the process when recovering ethanol. In addition,catalysts that are active for converting ethyl acetate to ethanol, thecatalysts may be deactivated by the presence of acetic acid or water.Deactivation of the catalyst causes a decrease in performance so theamount of acetic acid in the reaction mixture needs to be reduced beforethe mixture is exposed to the ethyl acetate converting catalyst.

Embodiments of the present invention provide advantageous solutions tothese problems to provide for effective ethanol production. When mixedfeeds, i.e. feeds containing acetic acid and ethyl acetate, are fed tothe first bed, the catalyst is preferably suited to converting bothacetic acid and ethyl acetate. Generally, acetic acid conversion may behigher than ethyl acetate conversion. In addition, the reactor streampasses from the first bed to the second bed without any purges of aceticacid or separation of the reactor stream. In one embodiment, hydrogen isfed, preferably in excess to the first bed, and any remaining hydrogenpasses along in the reactor stream to the second bed. Although it ispreferred to reduce the acetic acid fed to the second bed, in someembodiments, the process may convert ethyl acetate at higher rates thanacetic acid in the second bed in the presence of acetic acid. Thisallows the process of the present invention to efficiently produceethanol from acetic acid.

In one embodiment, the feed stream is a mixed feed comprising bothacetic acid and ethyl acetate. Preferably, the mixed feed comprises from5 to 40 wt. % ethyl acetate and from 60 to 95 wt. % acetic acid, andmore preferably from 10 to 30 wt. % ethyl acetate and 70 to 90 wt. %acetic acid. In one embodiment, the mixed feed comprises 30 wt. % ethylacetate and 70 wt. % acetic acid. In another embodiment, the mixed feedcomprises 15 wt. % ethyl acetate and 85 wt. % acetic acid. In stillanother embodiment, the mixed feed comprises 5 wt. % ethyl acetate and95 wt. % acetic acid.

Using a mixed feed, the hydrogenation in the stacked bed reactor mayachieve favorable conversion of acetic acid and ethyl acetate. For thepurposes of the present invention, the term “conversion” refers to thenet change of the flow of acetic acid or ethyl acetate into the multiplebed reactor as compared to the flow of acetic acid or ethyl acetate outof the stacked bed reactor. The net change may represent that the aceticacid and/or ethyl acetate are converted to a compound other than aceticacid or ethyl acetate, respectively. Conversion is expressed as apercentage based on acetic acid and/or ethyl acetate in the feed. Theconversion of acetic acid in the first bed may be at least 60%, at least70% or at least 80%. In some embodiments, a larger bed volume for thefirst bed may achieve an acetic acid conversion that is greater than97%, 98%, or 99%. Generally, acetic acid is not converted in the secondbed, and thus the conversion in the first bed is representative of theconversion of acetic acid in the stacked bed reactor. The conversion ofethyl acetate in the first bed preferably is greater than 0%, meaningthat more ethyl acetate is consumed than produced. During thehydrogenation of acetic acid in the first bed, ethyl acetate may beproduced and further converted in the second bed to ethanol. Thus,negative conversions of ethyl acetate, i.e. conversions less than 0%,may be tolerated in the first bed provided that the second bed convertsthe ethyl acetate to ethanol and there is no net increase of ethylacetate across the stacked bed. Thus the conversion of ethyl acetate inthe stacked bed reactor is greater than 0%, e.g., greater than 5%,greater than 25%, or greater than 50%. In an exemplary embodiment, theconversion of ethyl acetate in the second bed may range from 50 to 98%,e.g., from 60 to 95% or from 70 to 90%.

In one aspect, the mixed feed is converted to ethanol and ethyl acetate.Preferably, the selectivity to ethanol is greater than ethyl acetate andthe reactor stream from the first reactor bed contains lower ethylacetate concentrations than the feed stream, based on weight. Thus, thesecond reactor bed may react the remaining ethyl acetate while allowinga majority of the ethanol to pass through.

In another aspect, the mixed feed is converted mainly to ethyl acetatewith low ethanol concentrations, based on weight. In these embodiments,the second reactor bed may be used to convert the ethyl acetate toethanol.

In one embodiment, the feed stream may comprise essentially acetic acid.Preferably the acetic acid concentration is greater than 95 wt. %,greater than 97 wt. % or greater than 99 wt. %. In these embodiments,the feed stream may be referred to as an acetic acid feed stream. Theacetic acid feed stream may comprise other organics, includingaldehydes, ketones, and esters. Preferably for such embodiments, theacetic acid feed stream may be substantially free of ethyl acetate. Theconversion of the acetic acid feed stream may be at least 60%, at least70% or at least 80%. In some embodiments, acetic acid is converted toethanol and ethyl acetate. In other embodiments, acetic acid isconverted mainly to ethyl acetate.

The mixed feed or acetic acid feed stream is fed to a first bed. In oneembodiment, hydrogen may also be supplied to the first bed. In oneembodiment, the first bed comprises a first catalyst comprising platinumand tin on a first support. Platinum may be present in the catalyst inan amount from 0.1 to 10 wt. %, e.g. from 0.1 to 5 wt. %, or from 0.1 to3 wt. %. Tin may be present in an amount from 0.1 to 20 wt. %, e.g.,from 0.1 to 10 wt. %, or from 0.1 to 5 wt. %.

The first catalyst may also comprise one or more third metals selectedfrom the group consisting of cobalt, vanadium, tungsten, palladium,lanthanum, cesium, manganese, ruthenium, rhenium, gold, and nickel. Morepreferably, the one or more third metals are selected from the groupconsisting of cobalt, vanadium, palladium, and cesium. In oneembodiment, the first catalyst is substantially free of rhenium,tungsten, and/or molybdenum. The third metal, when present, may bepresent in the catalyst in an amount from 0.05 to 5 wt. %, e.g. from 0.1to 5 wt. %, or from 0.1 to 3 wt. %. Suitable metal combinations with thethird metals may include platinum/tin/palladium, platinum/tin/cobalt,platinum/tin/cesium, platinum/tin/palladium/cobalt, andplatinum/tin/palladium/cesium.

The first catalysts of the present invention may be on any suitablesupport material. In one embodiment, the support material may be aninorganic oxide. In one embodiment, the support material may be selectedfrom the group consisting of silica, silica/alumina, calciummetasilicate, pyrogenic silica, high purity silica, carbon, activatedcarbon, alumina, titiana, zirconia, graphite, zeolites, and mixturesthereof. Zeolites may include high silica zeolites (HSZ™ Tosoh Products)that contain more silica than alumina. Silica gel may be used as aprecursor for preparing silica containing supports. Preferably, thesupport material comprises silica, or silica/alumina. In one embodimentthe first catalyst preferably does not contain a zeolite support. Inpreferred embodiments, the support material for the first catalyst ispresent in an amount from 25 wt. % to 99 wt. %, e.g., from 30 wt. % to98 wt. % or from 35 wt. % to 95 wt. %.

The surface area of silicaceous support material, e.g., silica,preferably is at least 50 m²/g, e.g., at least 100 m²/g, at least 150m²/g, at least 200 m²/g or most preferably at least 250 m²/g. In termsof ranges, the silicaceous support material preferably has a surfacearea from 50 to 600 m²/g, e.g., from 100 to 500 m²/g or from 100 to 300m²/g. High surface area silica, as used throughout the application,refers to silica having a surface area of at least 250 m²/g. Forpurposes of the present specification, surface area refers to BETnitrogen surface area, meaning the surface area as determined by ASTMD6556-04, the entirety of which is incorporated herein by reference.

The silicaceous support material also preferably has an average porediameter from 5 to 100 nm, e.g., from 5 to 30 nm, from 5 to 25 nm orfrom about 5 to 10 nm, as determined by mercury intrusion porosimetry,and an average pore volume from 0.5 to 2.0 cm³/g, e.g., from 0.7 to 1.5cm³/g or from about 0.8 to 1.3 cm³/g, as determined by mercury intrusionporosimetry.

The morphology of the support material, and hence of the resultingcatalyst composition, may vary widely. In some exemplary embodiments,the morphology of the support material and/or of the catalystcomposition may be pellets, extrudates, spheres, spray driedmicrospheres, rings, pentarings, trilobes, quadrilobes, multi-lobalshapes, or flakes although cylindrical pellets are preferred.Preferably, the silicaceous support material has a morphology thatallows for a packing density from 0.1 to 1.0 g/cm³, e.g., from 0.2 to0.9 g/cm³ or from 0.5 to 0.8 g/cm³. In terms of size, the silica supportmaterial preferably has an average particle size, e.g., meaning thediameter for spherical particles or equivalent spherical diameter fornon-spherical particles, from 0.01 to 1.0 cm, e.g., from 0.1 to 0.5 cmor from 0.2 to 0.4 cm. Since the one or more active metal(s) that aredisposed on or within the support are generally very small in size,those active metals should not substantially impact the size of theoverall catalyst particles. Thus, the above particle sizes generallyapply to both the size of the support as well as to the final catalystparticles.

A preferred silica support material is SS61138 High Surface Area (HSA)Silica Catalyst Carrier from Saint-Gobain NorPro. The Saint-GobainNorPro SS61138 silica contains approximately 95 wt. % high surface areasilica; a surface area of about 250 m²/g; a median pore diameter ofabout 12 nm; an average pore volume of about 1.0 cm³/g as measured bymercury intrusion porosimetry and a packing density of about 0.352g/cm³.

A preferred silica/alumina support material is KA-160 (Süd Chemie)silica spheres having a nominal diameter of about 5 mm, a density ofabout 0.562 g/ml, in absorptivity of about 0.583 g H₂O/g support, asurface area of about 160 to 175 m²/g, and a pore volume of about 0.68ml/g.

The support material for the first catalyst may also comprise a supportmodifier. A support modifier may adjust the acidity of the supportmaterial. In one embodiment, the total weight of the support modifiersare present in an amount from 0.1 wt. % to 50 wt. %, e.g., from 0.2 wt.% to 25 wt. %, from 0.5 wt. % to 15 wt. %, or from 1 wt. % to 8 wt. %,based on the total weight of the catalyst.

Support modifiers may adjust the acidity of the support for the firstcatalyst. For example, the acid sites, e.g. Brønsted acid sites, on thesupport material may be adjusted by the support modifier to favorselectivity to ethanol during the hydrogenation of acetic acid. Theacidity of the support material may be adjusted by reducing the numberor reducing the availability of Brønsted acid sites on the supportmaterial. The support material may also be adjusted by having thesupport modifier change the pKa of the support material. Unless thecontext indicates otherwise, the acidity of a surface or the number ofacid sites thereupon may be determined by the technique described in F.Delannay, Ed., “Characterization of Heterogeneous Catalysts”; ChapterIII: Measurement of Acidity of Surfaces, p. 370-404; Marcel Dekker,Inc., N.Y. 1984, the entirety of which is incorporated herein byreference. In particular, the use of modified supports that adjusts theacidity of the support to make the support less acidic or more basicfavors formation of ethanol over other hydrogenation products.

In some embodiments, the support modifier may be an acidic modifier thatincreases the acidity of the catalyst. Suitable acidic support modifiersmay be selected from the group consisting of: oxides of Group IVBmetals, oxides of Group VB metals, oxides of Group VIB metals, oxides ofGroup VIIB metals, oxides of Group VIII metals, aluminum oxides, andmixtures thereof. Acidic support modifiers include those selected fromthe group consisting of TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅, Al₂O₃, B₂O₃, P₂O₅, andSb₂O₃. Preferred acidic support modifiers include those selected fromthe group consisting of TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅, and Al₂O₃. The acidicmodifier may also include those selected from the group consisting ofWO₃, MoO₃, Fe₂O₃, Cr₂O₃, V₂O₅, MnO₂, CuO, Co₂O₃, and Bi₂O₃.

In another embodiment, the support modifier may be a basic modifier thathas a low volatility or no volatility. Such basic modifiers, forexample, may be selected from the group consisting of: (i) alkalineearth metal oxides, (ii) alkali metal oxides, (iii) alkaline earth metalmetasilicates, (iv) alkali metal metasilicates, (v) Group IIB metaloxides, (vi) Group IIB metal metasilicates, (vii) Group IIIB metaloxides, (viii) Group IIIB metal metasilicates, and mixtures thereof. Inaddition to oxides and metasilicates, other types of modifiers includingnitrates, nitrites, acetates, and lactates may be used. Preferably, thesupport modifier is selected from the group consisting of oxides andmetasilicates of any of sodium, potassium, magnesium, calcium, scandium,yttrium, and zinc, as well as mixtures of any of the foregoing. Morepreferably, the basic support modifier is a calcium silicate, and evenmore preferably calcium metasilicate (CaSiO₃). If the basic supportmodifier comprises calcium metasilicate, it is preferred that at least aportion of the calcium metasilicate is in crystalline form.

The reactants, either the mixed feed or acetic acid feed stream, passthrough the first bed containing the first catalyst to produce a reactorstream. Hydrogen preferably passes through the first bed in the reactorstream so that it be may be consumed in the second bed. In oneembodiment, there is no separate hydrogen feed to the second bed.Depending on the selectivity, the reactor stream may comprise ethanoland ethyl acetate or mainly ethyl acetate. The reactor stream is passedover the second bed that contains the second catalyst. It should beunderstood that a reactor may have one or more first beds and one ormore second beds. Preferably, in the stacked bed reactor, the first andsecond beds are adjacent such that the reactor stream from the first bedpasses directly into the second bed.

The second bed may comprise a second catalyst that comprises copper oran oxide thereof. In one embodiment, the second catalyst may furthercomprise zinc, aluminum, cobalt, or oxides thereof. In some stacked bedsof the present invention, to achieve suitable ethyl acetate conversionand favorable ethanol selectivity, it is preferred that the secondcatalyst comprises copper and zinc or an oxide thereof. Copper may bepresent in an amount from 35 to 70 wt. % and more preferably 40 to 65wt. %. Zinc may be present in an amount from 15 to 40 wt. % and morepreferably 20 to 30 wt. %. Copper and zinc may be present as oxides. Inone embodiment, the second catalyst comprises greater than 65 wt. %copper and greater than 25 wt. % zinc. In another embodiment, the secondcatalyst comprises 41 wt. % copper and 26 wt. % zinc. In still anotherembodiment, the second catalyst comprises 60.8 wt. % copper and 28.8 wt.% zinc. The second catalyst may also comprise a third metal selectedfrom the group consisting of molybdenum, tin, iron, cobalt, vanadium,tungsten, palladium, platinum, lanthanum, cerium, manganese, ruthenium,rhenium, gold, and nickel. Preferably the third metal is not chromiumand the second catalyst may be substantially free of chromium.

The second catalysts of the present invention may be on any suitablesupport material. In one embodiment, the support material may be aninorganic oxide. In one embodiment, the support material may be selectedfrom the group consisting of silica, silica/alumina, alumina, titania,zeolites, and mixtures thereof. Preferably, the support material for thesecond catalyst comprises silica/alumina or alumina. In preferredembodiments, the support material for the second catalyst is present inan amount from 1 wt. % to 50 wt. %, e.g., from 1 wt. % to 30 wt. % orfrom 5 wt. % to 15 wt. %. In one embodiment, the support material forthe first and second catalysts may both comprise alumina.

For purposes of the present invention, the second catalyst is capable ofconverting ethyl acetate in the presence of acetic acid. Thus, the firstreactor bed does not need to achieve complete conversion of acetic acidand also there is no separate purge of acetic acid between the first andsecond bed. In one embodiment, the reactor stream from the first bed maycomprise less than 70 wt. % acetic acid, e.g., at less than 40 wt. %acetic acid or less than 20 wt. % acetic acid. In one embodiment, thereactor stream may comprise at least 5 wt. % acetic acid, e.g., at least10 wt. % acetic acid or at least 15 wt. % acetic acid.

In one embodiment, both the first and second beds may be in one vessel.In other embodiments, the stacked bed reactor may comprise separatevessels, each containing a first or second bed. The catalyst loading inthe first and second bed may vary. In terms of a volumetric ratio thefirst bed may contain more catalyst than the second bed, e.g., greaterthan 1.5:1, or greater than 2:1. In many embodiments of the presentinvention, an “adiabatic” stacked bed reactor may be used; that is,there is little or no need for internal plumbing through the reactionzone to add or remove heat.

The hydrogenation in the stacked bed reactor may be carried out ineither the liquid phase or vapor phase. Preferably, the reaction iscarried out in the vapor phase under the following conditions. Thereaction temperature may range from 125° C. to 350° C., e.g., from 200°C. to 325° C., from 225° C. to 300° C., or from 250° C. to 300° C. Thepressure may range from 10 kPa to 3000 kPa, e.g., from 50 kPa to 2300kPa, or from 100 kPa to 1500 kPa. The reactants may be fed to thereactor at a gas hourly space velocity (GHSV) of greater than 500 hr⁻¹,e.g., greater than 1000 hr⁻¹, greater than 2500 hr⁻¹ or even greaterthan 5000 hr⁻¹. In terms of ranges the GHSV may range from 50 hr⁻¹ to50,000 hr⁻¹, e.g., from 500 hr⁻¹ to 30,000 hr⁻¹, from 1000 hr⁻¹ to10,000 hr⁻¹, or from 1000 hr⁻¹ to 6500 hr⁻¹.

The hydrogenation optionally is carried out at a pressure justsufficient to overcome the pressure drop across the catalytic bed at theGHSV selected, although there is no bar to the use of higher pressures,it being understood that considerable pressure drop through the reactorbed may be experienced at high space velocities, e.g., 5000 hr⁻¹ or6,500 hr⁻¹.

Although the reaction consumes two moles of hydrogen per mole of aceticacid to produce one mole of ethanol, the actual molar ratio of hydrogento acetic acid in the feed stream may vary from about 100:1 to 1:100,e.g., from 50:1 to 1:50, from 20:1 to 1:2, or from 12:1 to 1:1. Mostpreferably, the molar ratio of hydrogen to acetic acid is greater than2:1, e.g., greater than 4:1 or greater than 8:1.

Contact or residence time can also vary widely, depending upon suchvariables as amount of acetic acid, catalyst, reactor, temperature, andpressure. Typical contact times range from a fraction of a second tomore than several hours when a catalyst system other than a fixed bed isused, with preferred contact times, at least for vapor phase reactions,from 0.1 to 100 seconds, e.g., from 0.3 to 80 seconds or from 0.4 to 30seconds.

Selectivity is expressed as a mole percent based on converted aceticacid and/or ethyl acetate fed to the first reactor bed. It should beunderstood that each compound converted from acetic acid and/or ethylacetate has an independent selectivity and that selectivity isindependent from conversion. For example, if 60 mole % of the convertedacetic acid is converted to ethanol, we refer to the ethanol selectivityas 60%. Total selectivity is based on the combined converted acetic acidand ethyl acetate. Preferably, the catalyst total selectivity to ethanolis at least 60%, e.g., at least 70%, or at least 80%. Preferably, thetotal selectivity to ethanol is at least 80%, e.g., at least 85% or atleast 88%. Preferred embodiments of the hydrogenation process also havelow selectivity to undesirable products, such as methane, ethane, andcarbon dioxide. The selectivity to these undesirable products preferablyis less than 4%, e.g., less than 2% or less than 1%. More preferably,these undesirable products are present in undetectable amounts.Formation of alkanes may be low, and ideally less than 2%, less than 1%,or less than 0.5% of the acetic acid passed over the catalyst isconverted to alkanes, which have little value other than as fuel.

In one embodiment, when an acetic acid stream is fed to the stacked bedreactor, the overall selectivity to methyl acetate is less than 5%,e.g., less than 3% or more preferably less than 2%. In one embodiment,substantially no methyl acetate is formed in the stacked bed reactor.

The term “productivity,” as used herein, refers to the grams of aspecified product, e.g., ethanol, formed during the hydrogenation basedon the kilograms of catalyst used per hour. For purposes of the presentinvention, productivity includes both the first and second catalyst. Aproductivity of at least 100 grams of ethanol per kilogram of catalystper hour, e.g., at least 400 grams of ethanol per kilogram of catalystper hour or at least 600 grams of ethanol per kilogram of catalyst perhour, is preferred. In terms of ranges, the productivity preferably isfrom 100 to 3,000 grams of ethanol per kilogram of catalyst per hour,e.g., from 400 to 2,500 grams of ethanol per kilogram of catalyst perhour or from 600 to 2,000 grams of ethanol per kilogram of catalyst perhour.

Operating under the conditions of the present invention may result inethanol production on the order of at least 0.1 tons of ethanol perhour, e.g., at least 1 ton of ethanol per hour, at least 5 tons ofethanol per hour, or at least 10 tons of ethanol per hour. Larger scaleindustrial production of ethanol, depending on the scale, generallyshould be at least 1 ton of ethanol per hour, e.g., at least 15 tons ofethanol per hour or at least 30 tons of ethanol per hour. In terms ofranges, for large scale industrial production of ethanol, the process ofthe present invention may produce from 0.1 to 160 tons of ethanol perhour, e.g., from 15 to 160 tons of ethanol per hour or from 30 to 80tons of ethanol per hour. Ethanol production from fermentation, due theeconomies of scale, typically does not permit the single facilityethanol production that may be achievable by employing embodiments ofthe present invention.

In various embodiments of the present invention, the crude ethanolproduct produced by the hydrogenation process, before any subsequentprocessing, such as purification and separation, will typically compriseethanol and water. Exemplary compositional ranges for the crude ethanolproduct are provided in Table 1. The “others” identified in Table 1 mayinclude, for example, esters, ethers, aldehydes, ketones, alkanes,higher alcohols, and carbon dioxide.

TABLE 1 CRUDE ETHANOL PRODUCT COMPOSITIONS Conc. Conc. Conc. Conc.Component (wt. %) (wt. %) (wt. %) (wt. %) Ethanol 5 to 72 15 to 72  15to 70 25 to 65 Acetic Acid 0 to 90 0 to 50  0 to 35  0 to 15 Water 5 to40 5 to 30 10 to 30 10 to 26 Ethyl Acetate 0 to 30 0 to 20  1 to 12  3to 10 Acetaldehyde 0 to 10 0 to 3  0.1 to 3  0.2 to 2  Others 0.1 to 10 0.1 to 6   0.1 to 4  —

In one embodiment, the crude ethanol product comprises acetic acid in anamount less than 20 wt. %, e.g., less than 15 wt. %, less than 10 wt. %or less than 5 wt. %. In terms of ranges, the acetic acid concentrationof Table 1 may range from 0.1 wt. % to 20 wt. %, e.g., 0.2 wt. % to 15wt. %, from 0.5 wt. % to 10 wt. % or from 1 wt. % to 5 wt. %. Inembodiments having lower amounts of acetic acid, the conversion ofacetic acid is preferably greater than 75%, e.g., greater than 85% orgreater than 90%. In addition, the selectivity to ethanol may also bepreferably high, and is preferably greater than 75%, e.g., greater than85% or greater than 90%.

The raw materials, acetic acid and hydrogen, used in connection with theprocess of this invention may be derived from any suitable sourceincluding natural gas, petroleum, coal, biomass, and so forth. Asexamples, acetic acid may be produced via methanol carbonylation,acetaldehyde oxidation, ethylene oxidation, oxidative fermentation, andanaerobic fermentation. Methanol carbonylation processes suitable forproduction of acetic acid are described in U.S. Pat. Nos. 7,208,624;7,115,772; 7,005,541; 6,657,078; 6,627,770; 6,143,930; 5,599,976;5,144,068; 5,026,908; 5,001,259; and 4,994,608, the entire disclosuresof which are incorporated herein by reference. Optionally, theproduction of ethanol may be integrated with such methanol carbonylationprocesses.

As petroleum and natural gas prices fluctuate becoming either more orless expensive, methods for producing acetic acid and intermediates suchas methanol and carbon monoxide from alternate carbon sources have drawnincreasing interest. In particular, when petroleum is relativelyexpensive, it may become advantageous to produce acetic acid fromsynthesis gas (“syngas”) that is derived from other available carbonsource. U.S. Pat. No. 6,232,352, the entirety of which is incorporatedherein by reference, for example, teaches a method of retrofitting amethanol plant for the manufacture of acetic acid. By retrofitting amethanol plant, the large capital costs associated with CO generationfor a new acetic acid plant are significantly reduced or largelyeliminated. All or part of the syngas is diverted from the methanolsynthesis loop and supplied to a separator unit to recover CO, which isthen used to produce acetic acid. In a similar manner, hydrogen for thehydrogenation step may be supplied from syngas.

In some embodiments, some or all of the raw materials for theabove-described acetic acid hydrogenation process may be derivedpartially or entirely from syngas. For example, the acetic acid may beformed from methanol and carbon monoxide, both of which may be derivedfrom syngas. The syngas may be formed by partial oxidation reforming orsteam reforming, and the carbon monoxide may be separated from syngas.Similarly, hydrogen that is used in the step of hydrogenating the aceticacid to form the crude ethanol product may be separated from syngas. Thesyngas, in turn, may be derived from variety of carbon sources. Thecarbon source, for example, may be selected from the group consisting ofnatural gas, oil, petroleum, coal, biomass, and combinations thereof.Syngas or hydrogen may also be obtained from bio-derived methane gas,such as bio-derived methane gas produced by landfills or agriculturalwaste.

In another embodiment, the acetic acid used in the hydrogenation stepmay be formed from the fermentation of biomass. The fermentation processpreferably utilizes an acetogenic process or a homoacetogenicmicroorganism to ferment sugars to acetic acid producing little, if any,carbon dioxide as a by-product. The carbon efficiency for thefermentation process preferably is greater than 70%, greater than 80% orgreater than 90% as compared to conventional yeast processing, whichtypically has a carbon efficiency of about 67%. Optionally, themicroorganism employed in the fermentation process is of a genusselected from the group consisting of Clostridium, Lactobacillus,Moorella, Thermoanaerobacter, Propionibacterium, Propionispera,Anaerobiospirillum, and Bacteriodes, and in particular, species selectedfrom the group consisting of Clostridium formicoaceticum, Clostridiumbutyricum, Moorella thermoacetica, Thermoanaerobacter kivui,Lactobacillus delbrukii, Propionibacterium acidipropionici,Propionispera arboris, Anaerobiospirillum succinicproducens, Bacteriodesamylophilus and Bacteriodes ruminicola. Optionally in this process, allor a portion of the unfermented residue from the biomass, e.g., lignans,may be gasified to form hydrogen that may be used in the hydrogenationstep of the present invention. Exemplary fermentation processes forforming acetic acid are disclosed in U.S. Pat. Nos. 6,509,180;6,927,048; 7,074,603; 7,507,562; 7,351,559; 7,601,865; 7,682,812; and7,888,082, the entireties of which are incorporated herein by reference.See also US Publ. Nos. 2008/0193989 and 2009/0281354, the entireties ofwhich are incorporated herein by reference.

Examples of biomass include, but are not limited to, agriculturalwastes, forest products, grasses, and other cellulosic material, timberharvesting residues, softwood chips, hardwood chips, tree branches, treestumps, leaves, bark, sawdust, off-spec paper pulp, corn, corn stover,wheat straw, rice straw, sugarcane bagasse, switchgrass, miscanthus,animal manure, municipal garbage, municipal sewage, commercial waste,grape pumice, almond shells, pecan shells, coconut shells, coffeegrounds, grass pellets, hay pellets, wood pellets, cardboard, paper,plastic, and cloth. See, e.g., U.S. Pat. No. 7,884,253, the entirety ofwhich is incorporated herein by reference. Another biomass source isblack liquor, a thick, dark liquid that is a byproduct of the Kraftprocess for transforming wood into pulp, which is then dried to makepaper. Black liquor is an aqueous solution of lignin residues,hemicellulose, and inorganic chemicals.

U.S. Pat. No. RE 35,377, also incorporated herein by reference, providesa method for the production of methanol by converting carbonaceousmaterials such as oil, coal, natural gas and biomass materials. Theprocess includes hydrogasification of solid and/or liquid carbonaceousmaterials to obtain a process gas which is steam pyrolized withadditional natural gas to form synthesis gas. The syngas is converted tomethanol which may be carbonylated to acetic acid. The method likewiseproduces hydrogen which may be used in connection with this invention asnoted above. U.S. Pat. No. 5,821,111, which discloses a process forconverting waste biomass through gasification into synthesis gas, andU.S. Pat. No. 6,685,754, which discloses a method for the production ofa hydrogen-containing gas composition, such as a synthesis gas includinghydrogen and carbon monoxide, are incorporated herein by reference intheir entireties.

Alternatively, acetic acid in vapor form may be taken directly as crudeproduct from the flash vessel of a methanol carbonylation unit of theclass described in U.S. Pat. No. 6,657,078, the entirety of which isincorporated herein by reference. The crude vapor product, for example,may be fed directly to the ethanol synthesis reaction zones of thepresent invention without the need for condensing the acetic acid andlight ends or removing water, saving overall processing costs.

Depending on the crude ethanol product composition from the stackedreactor bed, there may be several different processes for separating theimpurities and recovering ethanol. FIGS. 1-5 illustrate variousseparation schemes for recovering ethanol. The hydrogenation system 100in FIGS. 1-5 comprises reaction zone 101 and separation zone 102.Reaction zone comprises a stacked bed reactor 103 having a first bed 104and a second bed 105. First bed 104 comprises a first catalystcomprising platinum and tin as described above. Second bed 105 comprisessecond catalyst comprising copper or oxides thereof, as described above.

Hydrogen in line 106 and a reactant feed line 107 are fed to a vaporizer108 to create a vapor feed stream in line 109 that is directed tostacked bed reactor 103. Hydrogen feed line 106 may be preheated to atemperature from 30° C. to 150° C., e.g., from 50° C. to 125° C. or from60° C. to 115° C. Hydrogen feed line 106 may be fed at a pressure from1300 kPa to 3100 kPa, e.g., from 1500 kPa to 2800 kPa, or 1700 kPa to2600 kPa. Reactant in line 107 may comprise acetic acid and/or ethylacetate. In one embodiment, reactant in line 107 comprises greater than95 wt. % acetic acid. In another embodiment, reactant in line 107comprises from 5 to 40 wt. % ethyl acetate and 60 to 95 wt. % aceticacid, and more preferably from 5 to 30 wt. % ethyl acetate and 70 to 95wt. % acetic acid. The acetic acid and/or ethyl acetate may be recycledfrom within system 100 or is fresh. In one embodiment, lines 106 and 107may be combined and jointly fed to vaporizer 108 to form a vapor feedstream in line 109. The temperature of vapor feed stream in line 109 ispreferably from 100° C. to 350° C., e.g., from 120° C. to 310° C. orfrom 150° C. to 300° C. Any feed that is not vaporized is removed fromvaporizer 108 in blowdown stream 110 and may be recycled or discardedthereto. The mass ratio of vapor feed stream in line 109 to blowdownstream 110 may be from 6:1 to 500:1, e.g., from 10:1 to 500:1, from 20:1to 500:1 or from 50:1 to 500:1. In addition, although vapor feed streamin line 109 is shown as being directed to the top of stacked bed reactor103, line 109 may be directed to the side, upper portion, or bottom.More preferably, vapor feed stream in line 109 is fed to the first bed104.

In one embodiment, one or more guard beds (not shown) may be usedupstream of the reactor, optionally upstream of vaporizer 108, toprotect the catalyst from poisons or undesirable impurities contained inthe feed or return/recycle streams. Such guard beds may be employed inthe vapor or liquid streams. Suitable guard bed materials may include,for example, carbon, silica, alumina, ceramic, or resins. In one aspect,the guard bed media is functionalized, e.g., silver functionalized, totrap particular species such as sulfur or halogens.

In reactor 103, acetic acid and/or ethyl acetate is preferably reactedin first bed 104 and the reactor stream from first bed 104 is passedalong to second bed 105. In second bed 105, the ethyl acetate ispreferably reduced to ethanol. During the hydrogenation process, a crudeethanol product stream is withdrawn, preferably continuously, fromreactor 103 via line 111.

The crude ethanol product stream in line 111 may be condensed and fed toa separator 112, which, in turn, provides a vapor stream 113 and aliquid stream 114. In some embodiments, separator 112 may comprise aflasher or a knockout pot. Separator 112 may operate at a temperaturefrom 20° C. to 250° C., e.g., from 30° C. to 225° C. or from 60° C. to200° C. The pressure of separator 112 may be from 50 kPa to 2000 kPa,e.g., from 75 kPa to 1500 kPa or from 100 kPa to 1000 kPa. Optionally,the crude ethanol product in line 111 may pass through one or moremembranes to separate hydrogen and/or other non-condensable gases.

The vapor stream 113 exiting separator 112 may comprise hydrogen andhydrocarbons, and may be purged and/or returned to reaction zone 101.When returned to reaction zone 101, vapor stream 113 is combined withthe hydrogen feed 106 and co-fed to vaporizer 108. In some embodiments,the returned vapor stream 113 may be compressed before being combinedwith hydrogen feed 106.

In FIG. 1, the liquid stream 114 from separator 112 is withdrawn andintroduced in the lower part of first column 120, e.g., lower half orlower third. First column 120 is also referred to as an “acid separationcolumn.” In one embodiment, the contents of liquid stream 114 aresubstantially similar to the crude ethanol product obtained from thereactor, except that the composition has been depleted of hydrogen,carbon dioxide, methane and/or ethane, which are removed by separator112. Accordingly, liquid stream 114 may also be referred to as a crudeethanol product. Exemplary components of liquid stream 114 are providedin Table 2. It should be understood that liquid stream 114 may containother components, not listed in Table 2.

TABLE 2 COLUMN FEED COMPOSITION (Liquid Stream 114) Conc. (wt. %) Conc.(wt. %) Conc. (wt. %) Ethanol 5 to 72 10 to 70 15 to 65 Acetic Acid <90  0 to 50  0 to 35 Water 5 to 30  5 to 28 10 to 26 Ethyl Acetate <30 0.001 to 20    1 to 12 Acetaldehyde <10  0.001 to 3   0.1 to 3  Acetals0.01 to 10   0.01 to 6   0.01 to 5   Acetone <5 0.0005 to 0.05  0.001 to0.03  Other Esters <5 <0.005 <0.001 Other Ethers <5 <0.005 <0.001 OtherAlcohols <5 <0.005 <0.001

The amounts indicated as less than (<) in the tables throughout thepresent specification are preferably not present and if present may bepresent in trace amounts or in amounts greater than 0.0001 wt. %.

The “other esters” in Table 2 may include, but are not limited to, ethylpropionate, methyl acetate, isopropyl acetate, n-propyl acetate, n-butylacetate or mixtures thereof. The “other ethers” in Table 2 may include,but are not limited to, diethyl ether, methyl ethyl ether, isobutylethyl ether or mixtures thereof. The “other alcohols” in Table 2 mayinclude, but are not limited to, methanol, isopropanol, n-propanol,n-butanol, 2-butanol or mixtures thereof. In one embodiment, the liquidstream 114 may comprise propanol, e.g., isopropanol and/or n-propanol,in an amount from 0.001 to 0.1 wt. %, from 0.001 to 0.05 wt. % or from0.001 to 0.03 wt. %. In should be understood that these other componentsmay be carried through in any of the distillate or residue streamsdescribed herein and will not be further described herein, unlessindicated otherwise.

Optionally, crude ethanol product in line 111 or in liquid stream 114may be further fed to an esterification reactor, hydrogenolysis reactor,or combination thereof. An esterification reactor may be used to consumeresidual acetic acid present in the crude ethanol product to furtherreduce the amount of acetic acid that would otherwise need to beremoved. Hydrogenolysis may be used to convert ethyl acetate in thecrude ethanol product to ethanol.

In the embodiment shown in FIG. 1, line 114 is introduced in the lowerpart of first column 120, e.g., lower half or lower third. In firstcolumn 120, unreacted acetic acid, a portion of the water, and otherheavy components, if present, are removed from the composition in line121 and are withdrawn, preferably continuously, as residue. Some or allof the residue may be returned and/or recycled back to reaction zone 101via line 121. Recycling the acetic acid in line 121 to the vaporizer 108may reduce the amount of heavies that need to be purged from vaporizer108. Optionally, at least a portion of residue in line 121 may be purgedfrom the system. Reducing the amount of heavies to be purged may improveefficiencies of the process while reducing byproducts.

First column 120 also forms an overhead distillate, which is withdrawnin line 122, and which may be condensed and refluxed, for example, at aratio from 10:1 to 1:10, e.g., from 3:1 to 1:3 or from 1:2 to 2:1.

When column 120 is operated under standard atmospheric pressure, thetemperature of the residue exiting in line 121 preferably is from 95° C.to 120° C., e.g., from 110° C. to 117° C. or from 111° C. to 115° C. Thetemperature of the distillate exiting in line 122 preferably is from 70°C. to 110° C., e.g., from 75° C. to 95° C. or from 80° C. to 90° C.Column 120 preferably operates at ambient pressure. In otherembodiments, the pressure of first column 120 may range from 0.1 kPa to510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa. Exemplarycomponents of the distillate and residue compositions for first column120 are provided in Table 3 below. It should also be understood that thedistillate and residue may also contain other components, not listed,such as components in the feed. For convenience, the distillate andresidue of the first column may also be referred to as the “firstdistillate” or “first residue.” The distillates or residues of the othercolumns may also be referred to with similar numeric modifiers (second,third, etc.) in order to distinguish them from one another, but suchmodifiers should not be construed as requiring any particular separationorder.

TABLE 3 ACID COLUMN 120 (FIG. 1) Conc. (wt. %) Conc. (wt. %) Conc. (wt.%) Distillate Ethanol 20 to 75 30 to 70 40 to 65 Water 10 to 40 15 to 3520 to 35 Acetic Acid  <2 0.001 to 0.5  0.01 to 0.2  Ethyl Acetate <605.0 to 40  10 to 30 Acetaldehyde <10 0.001 to 5    0.01 to 4   Acetals0.01 to 10  0.05 to 6   0.1 to 5  Acetone    <0.05 0.001 to 0.03   0.01to 0.025 Residue Acetic Acid  60 to 100 70 to 95 85 to 92 Water <30  1to 20  1 to 15 Ethanol  <1 <0.9 <0.07

As shown in Table 3, without being bound by theory, it has surprisinglyand unexpectedly been discovered that when any amount of acetal isdetected in the feed that is introduced to the acid separation column120, the acetal appears to decompose in the column such that less oreven no detectable amounts are present in the distillate and/or residue.

The distillate in line 122 preferably comprises ethanol, ethyl acetate,and water, along with other impurities, which may be difficult toseparate due to the formation of binary and tertiary azeotropes. Tofurther separate distillate, line 122 is introduced to the second column123, also referred to as the “light ends column,” preferably in themiddle part of column 123, e.g., middle half or middle third. Preferablythe second column 123 is an extractive distillation column. In suchembodiments, an extraction agent, such as water, may be added to secondcolumn 123. If the extraction agent comprises water, it may be obtainedfrom an external source or from an internal return/recycle line from oneor more of the other columns.

The molar ratio of the water in the extraction agent to the ethanol inthe feed to the second column is preferably at least 0.5:1, e.g., atleast 1:1 or at least 3:1. In terms of ranges, preferred molar ratiosmay range from 0.5:1 to 8:1, e.g., from 1:1 to 7:1 or from 2:1 to 6.5:1.Higher molar ratios may be used but with diminishing returns in terms ofthe additional ethyl acetate in the second distillate and decreasedethanol concentrations in the second column residue.

In one embodiment, an additional extraction agent, such as water from anexternal source, dimethylsulfoxide, glycerine, diethylene glycol,1-naphthol, hydroquinone, N,N′-dimethylformamide, 1,4-butanediol;ethylene glycol-1,5-pentanediol; propylene glycol-tetraethyleneglycol-polyethylene glycol; glycerine-propylene glycol-tetraethyleneglycol-1,4-butanediol, ethyl ether, methyl formate, cyclohexane,N,N-dimethyl-1,3-propanediamine, N,N′-dimethylethylenediamine,diethylene triamine, hexamethylene diamine and 1,3-diaminopentane, analkylated thiopene, dodecane, tridecane, tetradecane and chlorinatedparaffins, may be added to second column 123. Some suitable extractionagents include those described in U.S. Pat. Nos. 4,379,028, 4,569,726,5,993,610 and 6,375,807, the entire contents and disclosure of which arehereby incorporated by reference.

In the embodiments of the present invention, without the use of anextractive agent, a larger portion of the ethanol would carry over intothe second distillate in line 127. By using an extractive agent insecond column 123, the separation of ethanol into the second residue inline 126 is facilitated thus increasing the yield of the overall ethanolproduct in the second residue in line 126.

Second column 123 may be a tray or packed column. In one embodiment,second column 123 is a tray column having from 5 to 70 trays, e.g., from15 to 50 trays or from 20 to 45 trays. Although the temperature andpressure of second column 123 may vary, when at atmospheric pressure thetemperature of the second residue exiting in line 126 preferably is from60° C. to 90° C., e.g., from 70° C. to 90° C. or from 80° C. to 90° C.The temperature of the second distillate exiting in line 127 from secondcolumn 123 preferably is from 50° C. to 90° C., e.g., from 60° C. to 80°C. or from 60° C. to 70° C. Column 123 may operate at atmosphericpressure. In other embodiments, the pressure of second column 123 mayrange from 0.1 kPa to 510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPato 375 kPa. Exemplary components for the distillate and residuecompositions for second column 123 are provided in Table 4 below. Itshould be understood that the distillate and residue may also containother components, not listed, such as components in the feed.

TABLE 4 SECOND COLUMN 123 (FIG. 1) Conc. (wt. %) Conc. (wt. %) Conc.(wt. %) Distillate Ethyl Acetate 10 to 99 25 to 95 50 to 93 Acetaldehyde<25 0.5 to 15  1 to 8 Water <25 0.5 to 20   4 to 16 Ethanol <30 0.001 to15   0.01 to 5   Acetal 0.01 to 20   1 to 20  5 to 20 Residue Water 30to 90 40 to 85 50 to 85 Ethanol 10 to 75 15 to 60 20 to 50 Ethyl Acetate <3 0.001 to 2   0.001 to 0.5  Acetic Acid   <0.5 0.001 to 0.3  0.001 to0.2 

In preferred embodiments, the recycling of the third residue promotesthe separation of ethyl acetate from the residue of the second column123. For example, the weight ratio of ethyl acetate in the secondresidue to second distillate preferably is less than 0.4:1, e.g., lessthan 0.2:1 or less than 0.1:1. In embodiments that use an extractivedistillation column with water as an extraction agent as the secondcolumn 123, the weight ratio of ethyl acetate in the second residue toethyl acetate in the second distillate approaches zero. Second residuemay comprise, for example, from 30% to 99.5% of the water and from 85 to100% of the acetic acid from line 122. The second distillate in line 127comprises ethyl acetate and additionally comprises water, ethanol,and/or acetaldehyde.

The weight ratio of ethanol in the second residue to second distillatepreferably is at least 3:1, e.g., at least 6:1, at least 8:1, at least10:1 or at least 15:1. All or a portion of the third residue is recycledto the second column. In one embodiment, all of the third residue may berecycled until process 100 reaches a steady state and then a portion ofthe third residue is recycled with the remaining portion being purgedfrom the system 100. The composition of the second residue will tend tohave lower amounts of ethanol than when the third residue is notrecycled. As the third residue is recycled, the composition of thesecond residue, as provided in Table 4, comprises less than 30 wt. % ofethanol, e.g., less than 20 wt. % or less than 15 wt. %. The majority ofthe second residue preferably comprises water. Notwithstanding thiseffect, the extractive distillation step advantageously also reduces theamount of ethyl acetate that is sent to the third column, which ishighly beneficial in ultimately forming a highly pure ethanol product.

As shown, the second residue from second column 123, which comprisesethanol and water, is fed via line 126 to third column 128, alsoreferred to as the “product column.” More preferably, the second residuein line 126 is introduced in the lower part of third column 128, e.g.,lower half or lower third. Third column 128 recovers ethanol, whichpreferably is substantially pure with respect to organic impurities andother than the azeotropic water content, as the distillate in line 129.The distillate of third column 128 preferably is refluxed as shown inFIG. 1, for example, at a reflux ratio from 1:10 to 10:1, e.g., from 1:3to 3:1 or from 1:2 to 2:1. The third residue in line 124, whichcomprises primarily water, preferably is returned to the second column123 as an extraction agent as described above. In one embodiment (notshown), a first portion of the third residue in line 124 is recycled tothe second column and a second portion is purged and removed from thesystem. In one embodiment, once the process reaches steady state, thesecond portion of water to be purged is substantially similar to theamount water formed in the hydrogenation of acetic acid. In oneembodiment, a portion of the third residue may be used to hydrolyze anyother stream, such as one or more streams comprising ethyl acetate.

Third column 128 is preferably a tray column as described above andoperates at atmospheric pressure or optionally at pressures above orbelow atmospheric pressure. The temperature of the third distillateexiting in line 129 preferably is from 50° C. to 110° C., e.g., from 70°C. to 100° C. or from 75° C. to 95° C. The temperature of the thirdresidue in line 124 preferably is from 15° C. to 100° C., e.g., from 30°C. to 90° C. or from 50° C. to 80° C. Exemplary components of thedistillate and residue compositions for third column 128 are provided inTable 5 below. It should be understood that the distillate and residuemay also contain other components, not listed, such as components in thefeed.

TABLE 5 THIRD COLUMN 128 (FIG. 1) Conc. (wt. %) Conc. (wt. %) Conc. (wt.%) Distillate Ethanol 75 to 96  80 to 96  85 to 96 Water <12 1 to 9  3to 8 Acetic Acid <12 0.0001 to 0.1   0.005 to 0.05 Ethyl Acetate <120.0001 to 0.05   0.005 to 0.025 Acetaldehyde <12 0.0001 to 0.1   0.005to 0.05 Acetal <12 0.0001 to 0.05  0.005 to 0.01 Residue Water 75 to 100 80 to 100  90 to 100 Ethanol   <0.8 0.001 to 0.5  0.005 to 0.05 EthylAcetate  <1 0.001 to 0.5  0.005 to 0.2  Acetic Acid  <2 0.001 to 0.5 0.005 to 0.2 

In one embodiment, the third residue in line 124 is withdrawn from thirdcolumn 128 at a temperature higher than the operating temperature of thesecond column 123.

Any of the compounds that are carried through the distillation processfrom the feed or crude reaction product generally remain in the thirddistillate in amounts of less 0.01 wt. %, based on the total weight ofthe third distillate composition, e.g., less than 0.05 wt. % or lessthan 0.02 wt. %. In one embodiment, one or more side streams may removeimpurities from any of the columns in the system 100. Preferably atleast one side stream is used to remove impurities from the third column128. The impurities may be purged and/or retained within the system 100.

The third distillate in line 129 may be further purified to form ananhydrous ethanol product stream, i.e., “finished anhydrous ethanol,”using one or more additional separation systems, such as, for example,distillation columns, adsorption units, membranes, or molecular sieves.Suitable adsorption units include pressure swing adsorption units andthermal swing adsorption unit.

Returning to second column 123, the second distillate preferably isrefluxed as shown in FIG. 1, optionally at a reflux ratio of 1:10 to10:1, e.g., from 1:5 to 5:1 or from 1:3 to 3:1. In one embodiment, atleast a portion of second distillate in line 127 is further processed infourth column 131, also referred to as the “acetaldehyde removalcolumn.” In fourth column 131, the second distillate is separated into afourth distillate, which comprises acetaldehyde, in line 132 and afourth residue, which comprises ethyl acetate, in line 133. The fourthdistillate preferably is refluxed at a reflux ratio from 1:20 to 20:1,e.g., from 1:15 to 15:1 or from 1:10 to 10:1, and at least a portion ofthe fourth distillate is returned to vaporizer 108. Additionally, atleast a portion of fourth distillate in line 132 may be purged. Withoutbeing bound by theory, since acetaldehyde may be reacted, e.g., byhydrogenation, to form ethanol, the recycling of a stream that containsacetaldehyde to the reaction zone increases the yield of ethanol anddecreases byproduct and waste generation. In another embodiment, theacetaldehyde may be collected and utilized, with or without furtherpurification, to make useful products including but not limited ton-butanol, 1,3-butanediol, and/or crotonaldehyde and derivatives.

The fourth residue of fourth column 131 may be purged via line 133. Thefourth residue primarily comprises ethyl acetate and ethanol, which maybe suitable for use as a solvent mixture or in the production of esters.In one preferred embodiment, the acetaldehyde is removed from the seconddistillate in fourth column 131 such that no detectable amount ofacetaldehyde is present in the residue of column 131.

Fourth column 131 is a tray column as described above and may operateabove atmospheric pressure. In one embodiment, the pressure is from 120kPa to 5,000 kPa, e.g., from 200 kPa to 4,500 kPa, or from 400 kPa to3,000 kPa. In a preferred embodiment the fourth column 131 may operateat a pressure that is higher than the pressure of the other columns.

The temperature of the fourth distillate exiting in line 132 preferablyis from 60° C. to 110° C., e.g., from 70° C. to 100° C. or from 75° C.to 95° C. The temperature of the residue in line 133 preferably is from70° C. to 115° C., e.g., from 80° C. to 110° C. or from 85° C. to 110°C. Exemplary components of the distillate and residue compositions forfourth column 131 are provided in Table 6 below. It should be understoodthat the distillate and residue may also contain other components, notlisted, such as components in the feed.

TABLE 6 FOURTH COLUMN 131 (FIG. 1) Conc. (wt. %) Conc. (wt. %) Conc.(wt. %) Distillate Acetaldehyde 2 to 80  2 to 50   5 to 40 Ethyl Acetate<90 30 to 80  40 to 75 Ethanol <30 0.001 to 25   0.01 to 20 Water <250.001 to 20   0.01 to 15 Residue Ethyl Acetate 40 to 100  50 to 100   60to 100 Ethanol <40 0.001 to 30   0.01 to 15 Water <25 0.001 to 20     2to 15 Acetaldehyde  <1 0.001 to 0.5  Not detectable Acetal  <3 0.0001 to2     0.001 to 0.01

In one embodiment, a portion of the third residue in line 124 isrecycled to second column 123. In one embodiment, recycling the thirdresidue further reduces the aldehyde components in the second residueand concentrates these aldehyde components in second distillate in line127 and thereby sent to fourth column 131, wherein the aldehydes may bemore easily separated. The third distillate in line 129 may have lowerconcentrations of aldehydes and esters due to the recycling of thirdresidue in line 124.

FIG. 2 illustrates another exemplary separation system. The reactionzone 101 of FIG. 2 is similar to FIG. 1 and produces a liquid stream114, e.g., crude ethanol product, for further separation. In onepreferred embodiment, the reaction zone 101 of FIG. 2, in particularfirst bed 104, operates at above 80% acetic acid conversion, e.g., above90% conversion or above 99% conversion. Thus, the acetic acidconcentration in the liquid stream 114 may be low.

Liquid stream 114 is introduced in the middle or lower portion of afirst column 150, also referred to as acid-water column. For purposes ofconvenience, the columns in each exemplary separation process, may bereferred as the first, second, third, etc., columns, but it isunderstood that first column 150 in FIG. 2 operates differently than thefirst column 120 of FIG. 1. In one embodiment, no entrainers are addedto first column 150. In FIG. 2, first column 150, water and unreactedacetic acid, along with any other heavy components, if present, areremoved from liquid stream 114 and are withdrawn, preferablycontinuously, as a first residue in line 151. Preferably, a substantialportion of the water in the crude ethanol product that is fed to firstcolumn 150 may be removed in the first residue, for example, up to about75% or to about 90% of the water from the crude ethanol product. Firstcolumn 150 also forms a first distillate, which is withdrawn in line152.

When column 150 is operated under about 170 kPa, the temperature of theresidue exiting in line 151 preferably is from 90° C. to 130° C., e.g.,from 95° C. to 120° C. or from 100° C. to 115° C. The temperature of thedistillate exiting in line 152 preferably is from 60° C. to 90° C.,e.g., from 65° C. to 85° C. or from 70° C. to 80° C. In someembodiments, the pressure of first column 150 may range from 0.1 kPa to510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa.

The first distillate in line 152 comprises water, in addition to ethanoland other organics. In terms of ranges, the concentration of water inthe first distillate in line 152 preferably is from 4 wt. % to 38 wt. %,e.g., from 7 wt. % to 32 wt. %, or from 7 to 25 wt. %. A portion offirst distillate in line 153 may be condensed and refluxed, for example,at a ratio from 10:1 to 1:10, e.g., from 3:1 to 1:3 or from 1:2 to 2:1.It is understood that reflux ratios may vary with the number of stages,feed locations, column efficiency and/or feed composition. Operatingwith a reflux ratio of greater than 3:1 may be less preferred becausemore energy may be required to operate the first column 150. Thecondensed portion of the first distillate may also be fed to a secondcolumn 154.

The remaining portion of the first distillate in 152 is fed to a waterseparation unit 156. Water separation unit 156 may be an adsorptionunit, membrane, molecular sieves, extractive column distillation, or acombination thereof. A membrane or an array of membranes may also beemployed to separate water from the distillate. The membrane or array ofmembranes may be selected from any suitable membrane that is capable ofremoving a permeate water stream from a stream that also comprisesethanol and ethyl acetate.

In a preferred embodiment, water separator 156 is a pressure swingadsorption (PSA) unit. The PSA unit is optionally operated at atemperature from 30° C. to 160° C., e.g., from 80° C. to 140° C., and apressure from 0.01 kPa to 550 kPa, e.g., from 1 kPa to 150 kPa. The PSAunit may comprise two to five beds. Water separator 156 may remove atleast 95% of the water from the portion of first distillate in line 152,and more preferably from 99% to 99.99% of the water from the firstdistillate, in a water stream 157. All or a portion of water stream 157may be returned to column 150 in line 158, where the water preferably isultimately recovered from column 150 in the first residue in line 151.Additionally or alternatively, all or a portion of water stream 157 maybe purged via line 159. The remaining portion of first distillate exitsthe water separator 156 as ethanol mixture stream 160. Ethanol mixturestream 160 may have a low concentration of water of less than 10 wt. %,e.g., less than 6 wt. % or less than 2 wt. %. Exemplary components ofethanol mixture stream 160 and first residue in line 151 are provided inTable 7 below. It should also be understood that these streams may alsocontain other components, not listed, such as components derived fromthe feed.

TABLE 7 FIRST COLUMN 150 WITH PSA (FIG. 2) Conc. (wt. %) Conc. (wt. %)Conc. (wt. %) Ethanol Mixture Stream Ethanol 20 to 95 30 to 95 40 to 95Water <10 0.01 to 6   0.1 to 2  Acetic Acid  <2 0.001 to 0.5  0.01 to0.2  Ethyl Acetate <60  1 to 55  5 to 55 Acetaldehyde <10 0.001 to 5  0.01 to 4   Acetal   <0.1 <0.1 <0.05 Acetone   <0.05 0.001 to 0.03  0.01 to 0.025 Residue Acetic Acid <90  1 to 50  2 to 35 Water  30 to100 45 to 95 60 to 90 Ethanol  <1 <0.9 <0.3 

Preferably, ethanol mixture stream 160 is not returned or refluxed tofirst column 150. The condensed portion of the first distillate in line153 may be combined with ethanol mixture stream 160 to control the waterconcentration fed to the second column 154. For example, in someembodiments the first distillate may be split into equal portions, whilein other embodiments, all of the first distillate may be condensed orall of the first distillate may be processed in the water separationunit. In FIG. 2, the condensed portion in line 153 and ethanol mixturestream 160 are co-fed to second column 154. In other embodiments, thecondensed portion in line 153 and ethanol mixture stream 160 may beseparately fed to second column 154. The combined distillate and ethanolmixture has a total water concentration of greater than 0.5 wt. %, e.g.,greater than 2 wt. % or greater than 5 wt. %. In terms of ranges, thetotal water concentration of the combined distillate and ethanol mixturemay be from 0.5 to 15 wt. %, e.g., from 2 to 12 wt. %, or from 5 to 10wt. %.

The second column 154 in FIG. 2, also referred to as the “light endscolumn,” removes ethyl acetate and acetaldehyde from the firstdistillate in line 153 and/or ethanol mixture stream 160. Ethyl acetateand acetaldehyde are removed as a second distillate in line 161 andethanol is removed as the second residue in line 162. Second column 108may be a tray column or packed column. In one embodiment, second column154 is a tray column having from 5 to 70 trays, e.g., from 15 to 50trays or from 20 to 45 trays.

Second column 154 operates at a pressure ranging from 0.1 kPa to 510kPa, e.g., from 10 kPa to 450 kPa or from 50 kPa to 350 kPa. Althoughthe temperature of second column 154 may vary, when at about 20 kPa to70 kPa, the temperature of the second residue exiting in line 162preferably is from 30° C. to 75° C., e.g., from 35° C. to 70° C. or from40° C. to 65° C. The temperature of the second distillate exiting inline 161 preferably is from 20° C. to 55° C., e.g., from 25° C. to 50°C. or from 30° C. to 45° C.

The total concentration of water fed to second column 154 preferably isless than 10 wt. %, as discussed above. When first distillate in line153 and/or ethanol mixture stream comprises minor amounts of water,e.g., less than 1 wt. % or less than 0.5 wt. %, additional water may befed to the second column 154 as an extractive agent in the upper portionof the column. A sufficient amount of water is preferably added via theextractive agent such that the total concentration of water fed tosecond column 154 is from 1 to 10 wt. % water, e.g., from 2 to 6 wt. %,based on the total weight of all components fed to second column 154. Ifthe extractive agent comprises water, the water may be obtained from anexternal source or from an internal return/recycle line from one or moreof the other columns or water separators.

Suitable extractive agents may also include, for example,dimethylsulfoxide, glycerine, diethylene glycol, 1-naphthol,hydroquinone, N,N′-dimethylformamide, 1,4-butanediol; ethyleneglycol-1,5-pentanediol; propylene glycol-tetraethyleneglycol-polyethylene glycol; glycerine-propylene glycol-tetraethyleneglycol-1,4-butanediol, ethyl ether, methyl formate, cyclohexane,N,N-dimethyl-1,3-propanediamine, N,N′-dimethylethylenediamine,diethylene triamine, hexamethylene diamine and 1,3-diaminopentane, analkylated thiopene, dodecane, tridecane, tetradecane, chlorinatedparaffins, or a combination thereof. When extractive agents are used, asuitable recovery system, such as a further distillation column, may beused to recycle the extractive agent.

Exemplary components for the second distillate and second residuecompositions for the second column 154 are provided in Table 8, below.It should be understood that the distillate and residue may also containother components, not listed in Table 8.

TABLE 8 SECOND COLUMN 154 (FIG. 2) Conc. (wt. %) Conc. (wt. %) Conc.(wt. %) Second Distillate Ethyl Acetate 5 to 90  10 to 80 15 to 75Acetaldehyde <60  1 to 40  1 to 35 Ethanol <45 0.001 to 40   0.01 to 35 Water <20 0.01 to 10  0.1 to 5  Second Residue Ethanol 80 to 99.5 85 to97 60 to 95 Water <20 0.001 to 15   0.01 to 10  Ethyl Acetate  <1 0.001to 2    0.001 to 0.5  Acetic Acid   <0.5 <0.01 0.001 to 0.01  Acetal  <0.05 <0.03 <0.01

The second residue in FIG. 2 comprises one or more impurities selectedfrom the group consisting of ethyl acetate, acetic acid, andacetaldehyde. The second residue may comprise at least 100 wppm of theseimpurities, e.g., at least 250 wppm or at least 500 wppm. In someembodiments, the second residue may contain substantially no ethylacetate or acetaldehyde.

The second distillate in line 161, which comprises ethyl acetate and/oracetaldehyde, preferably is refluxed as shown in FIG. 2, for example, ata reflux ratio from 1:30 to 30:1, e.g., from 1:10 to 10:1 or from 1:3 to3:1. Additionally, at least a portion of second distillate 161 may bepurged.

FIG. 3 illustrates another exemplary separation system. The reactionzone 101 of FIG. 3 is similar to FIG. 1 and produces a liquid stream114, e.g., crude ethanol product, for further separation. In onepreferred embodiment, the reaction zone 101 of FIG. 3, in particularfirst bed 104, operates at above 80% acetic acid conversion, e.g., above90% conversion or above 99% conversion. Thus, the acetic acidconcentration in the liquid stream 114 may be low.

In the exemplary embodiment shown in FIG. 3, liquid stream 114 isintroduced in the lower part of first column 170, e.g., lower half ormiddle third. In one embodiment, no entrainers are added to first column170. In first column 170, a weight majority of the ethanol, water,acetic acid, and other heavy components, if present, are removed fromliquid stream 114 and are withdrawn, preferably continuously, as residuein line 171. First column 170 also forms an overhead distillate, whichis withdrawn in line 172, and which may be condensed and refluxed, forexample, at a ratio from 30:1 to 1:30, e.g., from 10:1 to 1:10 or from1:5 to 5:1. The overhead distillate in stream 172 preferably comprises aweight majority of the ethyl acetate from liquid stream 114.

When column 170 is operated under about 170 kPa, the temperature of theresidue exiting in line 171 preferably is from 70° C. to 155° C., e.g.,from 90° C. to 130° C. or from 100° C. to 110° C. The base of column 170may be maintained at a relatively low temperature by withdrawing aresidue stream comprising ethanol, water, and acetic acid, therebyproviding an energy efficiency advantage. The temperature of thedistillate exiting in line 172 from column 170 preferably at 170 kPa isfrom 75° C. to 100° C., e.g., from 75° C. to 83° C. or from 81° C. to84° C. In some embodiments, the pressure of first column 170 may rangefrom 0.1 kPa to 510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to375 kPa. Exemplary components of the distillate and residue compositionsfor first column 170 are provided in Table 9 below. It should also beunderstood that the distillate and residue may also contain othercomponents, not listed in Table 9.

TABLE 9 FIRST COLUMN 170 (FIG. 3) Conc. (wt. %) Conc. (wt. %) Conc. (wt.%) Distillate Ethyl Acetate 10 to 85 15 to 80 20 to 75 Acetaldehyde 0.1to 70  0.2 to 65  0.5 to 65  Diethyl Acetal 0.01 to 10  0.01 to 6   0.01to 5   Acetone <0.05 0.001 to 0.03   0.01 to 0.025 Ethanol  3 to 55  4to 50  5 to 45 Water 0.1 to 20   1 to 15  2 to 10 Acetic Acid <2   <0.1<0.05 Residue Acetic Acid 0.01 to 35  0.1 to 30  0.2 to 25  Water  5 to40 10 to 35 15 to 30 Ethanol 10 to 75 15 to 70 20 to 65

In an embodiment of the present invention, column 170 may be operated ata temperature where most of the water, ethanol, and acetic acid areremoved from the residue stream and only a small amount of ethanol andwater is collected in the distillate stream due to the formation ofbinary and tertiary azeotropes. The weight ratio of water in the residuein line 171 to water in the distillate in line 172 may be greater than1:1, e.g., greater than 2:1. The weight ratio of ethanol in the residueto ethanol in the distillate may be greater than 1:1, e.g., greater than2:1

The amount of acetic acid in the first residue may vary dependingprimarily on the conversion in stacked bed reactor 103. In oneembodiment, when the conversion is high, e.g., greater than 90%, theamount of acetic acid in the first residue may be less than 10 wt. %,e.g., less than 5 wt. % or less than 2 wt. %. In other embodiments, whenthe conversion is lower, e.g., less than 90%, the amount of acetic acidin the first residue may be greater than 10 wt. %.

The distillate preferably is substantially free of acetic acid, e.g.,comprising less than 1000 wppm, less than 500 wppm or less than 100 wppmacetic acid. The distillate may be purged from the system or recycled inwhole or part to reactor 103. In some embodiments, the distillate may befurther separated, e.g., in a distillation column (not shown), into anacetaldehyde stream and an ethyl acetate stream. Either of these streamsmay be returned to the reactor 103 or separated from system 100 as aseparate product.

Some species, such as acetals, may decompose in first column 170 suchthat very low amounts, or even no detectable amounts, of acetals remainin the distillate or residue.

To recover ethanol, the residue in line 171 may be further separated ina second column 173, also referred to as an “acid separation column.” Anacid separation column may be used when the acetic acid concentration inthe first residue is greater than 1 wt. %, e.g., greater than 5 wt. %.The first residue in line 171 is introduced to second column 173preferably in the top part of column 173, e.g., top half or top third.Second column 173 yields a second residue in line 174 comprising aceticacid and water, and a second distillate in line 175 comprising ethanol.Second column 173 may be a tray column or packed column. In oneembodiment, second column 173 is a tray column having from 5 to 150trays, e.g., from 15 to 50 trays or from 20 to 45 trays. Although thetemperature and pressure of second column 173 may vary, when atatmospheric pressure the temperature of the second residue exiting inline 174 preferably is from 95° C. to 130° C., e.g., from 100° C. to125° C. or from 110° C. to 120° C. The temperature of the seconddistillate exiting in line 175 preferably is from 60° C. to 100° C.,e.g., from 75° C. to 100° C. or from 80° C. to 100° C. The pressure ofsecond column 173 may range from 0.1 kPa to 510 kPa, e.g., from 1 kPa to475 kPa or from 1 kPa to 375 kPa. Exemplary components for thedistillate and residue compositions for second column 173 are providedin Table 10 below. It should be understood that the distillate andresidue may also contain other components, not listed in Table 10.

TABLE 10 SECOND COLUMN 173 (FIG. 3) Conc. (wt. %) Conc. (wt. %) Conc.(wt. %) Second Distillate Ethanol  70 to 99.9 75 to 98 80 to 95 EthylAcetate <10  0.001 to 5   0.01 to 3   Acetaldehyde <5 0.001 to 1   0.005to 0.5  Acetal 0.01 to 10  0.01 to 6   0.01 to 5   Water 0.1 to 30   1to 25  5 to 20 Second Residue Acetic Acid 0.1 to 45  0.2 to 40  0.5 to35  Water  45 to 100  55 to 99.8  65 to 99.5 Ethyl Acetate <2 <1 <0.5Ethanol <5 0.001 to 5   <2 

The weight ratio of ethanol in the second distillate in line 175 toethanol in the second residue in line 174 preferably is at least 35:1.In one embodiment, the weight ratio of water in the second residue 174to water in the second distillate 175 is greater than 2:1, e.g., greaterthan 4:1 or greater than 6:1. In addition, the weight ratio of aceticacid in the second residue 174 to acetic acid in the second distillate175 preferably is greater than 10:1, e.g., greater than 15:1 or greaterthan 20:1. Preferably, the second distillate in line 175 issubstantially free of acetic acid and may only contain, if any, traceamounts of acetic acid.

As shown, the second distillate in line 175 is fed to a third column176, e.g., ethanol product column, for separating the second distillateinto a third distillate (ethyl acetate distillate) in line 178 and athird residue (ethanol residue) in line 177. Second distillate in line175 may be introduced into the lower part of column 176, e.g., lowerhalf or lower third. Third distillate 178 is preferably refluxed, forexample, at a reflux ratio greater than 2:1, e.g., greater than 5:1 orgreater than 10:1. Additionally, at least a portion of third distillate178 may be purged. Third column 176 is preferably a tray column asdescribed herein and preferably operates at atmospheric pressure. Thetemperature of the third residue exiting from third column 176preferably is from 60° C. to 110° C., e.g., from 70° C. to 100° C. orfrom 75° C. to 95° C. The temperature of the third distillate exitingfrom third column 176 preferably is from 70° C. to 115° C., e.g., from80° C. to 110° C. or from 85° C. to 105° C., when the column is operatedat atmospheric pressure.

In one embodiment, third distillate in line 178 may be introduced intofirst column 170.

The remaining water from the second distillate in line 175 may beremoved in further embodiments of the present invention. Depending onthe water concentration, the ethanol product may be derived from thesecond distillate in line 175 or the third residue in line 177 Someapplications, such as industrial ethanol applications, may toleratewater in the ethanol product, while other applications, such as fuelapplications, may require an anhydrous ethanol. The amount of water inthe distillate of line 175 or the residue of line 177 may be closer tothe azeotropic amount of water, e.g., at least 4 wt. %, preferably lessthan 20 wt. %, e.g., less than 12 wt. % or less than 7.5 wt. %. Watermay be removed from the second distillate in line 175 or the thirdresidue in line 177 using several different separation techniques asdescribed herein. Particularly preferred techniques include the use ofdistillation column, membranes, adsorption units, and combinationsthereof.

Some of the residues withdrawn from the separation zone 102 compriseacetic acid and water. Depending on the amount of water and acetic acidcontained in the residue of first column, e.g., 120 in FIG. 1, 150 inFIG. 2, or residue of second column 173 in FIG. 3, the residue may betreated in one or more of the following processes. The following areexemplary processes for further treating the residue and it should beunderstood that any of the following may be used regardless of aceticacid concentration. When the residue comprises a majority of aceticacid, e.g., greater than 70 wt. %, the residue may be recycled to thereactor without any separation of the water. In one embodiment, theresidue may be separated into an acetic acid stream and a water streamwhen the residue comprises a majority of acetic acid, e.g., greater than50 wt. %. Acetic acid may also be recovered in some embodiments from theresidue having a lower acetic acid concentration. The residue may beseparated into the acetic acid and water streams by a distillationcolumn or one or more membranes. If a membrane or an array of membranesis employed to separate the acetic acid from the water, the membrane orarray of membranes may be selected from any suitable acid resistantmembrane that is capable of removing a permeate water stream. Theresulting acetic acid stream optionally is returned to the reactor 108.The resulting water stream may be used as an extractive agent or tohydrolyze an ester-containing stream in a hydrolysis unit.

In other embodiments, for example, where the residue comprises less than50 wt. % acetic acid, possible options include one or more of: (i)returning a portion of the residue to reactor 108, (ii) neutralizing theacetic acid, (iii) reacting the acetic acid with an alcohol, or (iv)disposing of the residue in a waste water treatment facility. It alsomay be possible to separate a residue comprising less than 50 wt. %acetic acid using a weak acid recovery distillation column to which asolvent (optionally acting as an azeotroping agent) may be added.Exemplary solvents that may be suitable for this purpose include ethylacetate, propyl acetate, isopropyl acetate, butyl acetate, vinylacetate, diisopropyl ether, carbon disulfide, tetrahydrofuran,isopropanol, ethanol, and C₃-C₁₂ alkanes. When neutralizing the aceticacid, it is preferred that the residue comprises less than 10 wt. %acetic acid. Acetic acid may be neutralized with any suitable alkali oralkaline earth metal base, such as sodium hydroxide or potassiumhydroxide. When reacting acetic acid with an alcohol, it is preferredthat the residue comprises less than 50 wt. % acetic acid. The alcoholmay be any suitable alcohol, such as methanol, ethanol, propanol,butanol, or mixtures thereof. The reaction forms an ester that may beintegrated with other systems, such as carbonylation production or anester production process. Preferably, the alcohol comprises ethanol andthe resulting ester comprises ethyl acetate. Optionally, the resultingester may be fed to the hydrogenation reactor.

In some embodiments, when the residue comprises very minor amounts ofacetic acid, e.g., less than 5 wt. % or less than 1 wt. %, the residuemay be neutralized and/or diluted before being disposed of to a wastewater treatment facility. The organic content, e.g., acetic acidcontent, of the residue beneficially may be suitable to feedmicroorganisms used in a waste water treatment facility.

In some embodiments, liquid stream 114 may contain substantially noacetic acid. In FIGS. 4 and 5, liquid stream 114 may be fed to a firstcolumn 180 for separating ethanol and ethyl acetate. In FIG. 5, there isan additional heavy column to remove any heavies from the ethanolproduct.

Liquid stream 114 is introduced to the side of a first distillationcolumn 180, also referred to as a “light ends column,” to yield a firstdistillate in line 181 comprising ethyl acetate and a first residue inline 182 comprising ethanol. Preferably the distillation column operatesto maintain a low concentration of ethyl acetate in the residue, e.g.,less than 1 wt. %, less than 0.1 wt. % or less than 0.01 wt. %. Thedistillate of column 180 preferably is refluxed at a ratio sufficient tomaintain low concentrations of ethyl acetate in the residue and minimizeethanol concentrations in the distillate, and reflux ratio may vary from30:1 to 1:30, e.g., from 10:1 to 1:10 or from 5:1 to 1:5.

Distillation column 180 may be a tray column or packed column. In oneembodiment, distillation column 180 is a tray column having from 5 to110 trays, e.g., from 15 to 90 trays or from 20 to 80 trays.Distillation column 180 operates at a pressure ranging from 20 kPa to500 kPa, e.g., from 50 kPa to 300 kPa or from 80 kPa to 200 kPa. Withoutbeing bound by theory, lower pressures of less than 100 kPa or less than70 kPa, may further enhance separation of liquid stream 114. Althoughthe temperature of distillation column 180 may vary, when at atmosphericpressure, the temperature of the distillate exiting in line 181preferably is from 40° C. to 90° C., e.g., from 45° C. to 85° C. or from50° C. to 80° C. The temperature of the residue exiting in line 182preferably is from 45° C. to 95° C., e.g., from 50° C. to 90° C. or from60° C. to 85° C.

Exemplary compositions of the first column 180 are shown in Table 11below. It should be understood that the distillate and residue may alsocontain other components, not listed in Table 11.

TABLE 11 FIRST COLUMN 180 (FIG. 4) Conc. (wt. %) Conc. (wt. %) Conc.(wt. %) Distillate Ethyl Acetate 20 to 80 25 to 75 30 to 70 Ethanol 0.01to 45   1 to 35  2 to 30 Water <10  <5  <3  Acetaldehyde 0.01 to 30  0.1to 20   1 to 10 Isopropanol 0.001 to 0.5  0.001 to 0.1  0.001 to 0.05 Acetone 0.001 to 3   0.001 to 1   0.001 to 0.5  Diethyl acetal 0.001 to3   0.001 to 1   0.01 to 0.5  Carbon Gases 0.001 to 2   0.001 to 1  0.001 to 0.5  Residue Ethanol  80 to 99.5  85 to 99.5  90 to 99.5 Water<20  0.001 to 15   0.01 to 10  Ethyl Acetate   <0.01  <0.001   <0.0001Isopropanol 0.001 to 3   0.001 to 1   0.001 to 0.5  Acetone 0.001 to 3  0.001 to 1   0.001 to 0.5  Diethyl acetal 0.001 to 3   0.001 to 1   0.01to 0.5  2-butanol 0.001 to 3   0.01 to 1   0.01 to 0.5  n-butanol <1<0.5 <0.1 Heavies <1 <0.5 <0.1

Without being bound by theory, the presence of acetaldehyde in the crudereaction mixture from the hydrogenolysis reactor may produce severaldifferent impurities. The heavy impurities, such as higher alcohols, maybuild up in the first residue. In particular, 2-butanol has been foundto be an impurity in this process. The weight ratio of 2-butanol ton-butanol in the first residue may be greater than 2:1, e.g., greaterthan 3:1 or greater than 5:1. Depending on the intended use of ethanol,these impurities may be of less significance. However, when a purerethanol product is desired, a portion of first residue may be furtherseparated in a finishing column 183 as shown in FIG. 5.

In some embodiments, it may be necessary to further treat the firstresidue to remove additional heavy compounds such as higher alcohols andany light components from the ethanol. As shown in FIG. 5, there isprovided a finishing column 183, also referred to as a “second column.”First residue in line 182 is fed to a lower portion of second column183. Second column 183 produces an ethanol sidestream in line 186, asecond distillate in line 184 and a second residue in line 185.Preferably ethanol sidestream in line 186 is the largest streamwithdrawn from fourth column 183 and is withdrawn at a point above thefeed point of the first residue in line 182. In one embodiment therelative flow ratios of sidestream to residue is greater than 50:1,e.g., greater than 100:1 or greater than 150:1.

Ethanol sidestream 186 preferably comprises at least 90% ethanol, e.g.,at least 92% ethanol and a least 95% ethanol. Water concentration inethanol sidestream 186 may be less than 10 wt. %, e.g., less than 5 wt.% or less than 1 wt. %. In addition, the amount of other impurities, inparticular diethyl acetal and 2-butanol, are preferably less than 0.05wt. %, e.g., less than 0.03 wt. % or less than 0.01 wt. %. The seconddistillate in line 184 preferably comprises a weight majority of thediethyl acetal fed to second column 183. In addition, other lightcomponents, such as acetaldehyde and/or ethyl acetate may alsoconcentrate in the second distillate. The second residue in line 185preferably comprises a weight majority of the 2-butanol fed to secondcolumn 183. Heavier alcohols may also concentrate in the fourth residuein line 185.

Second column 183 may be a tray column or packed column. In oneembodiment, Second column 183 is a tray column having from 10 to 100trays, e.g., from 20 to 80 trays or from 30 to 70 trays. Second column183 operates at a pressure ranging from 1 kPa to 510 kPa, e.g., from 10kPa to 450 kPa or from 50 kPa to 350 kPa. Although the temperature ofsecond column 183 may vary, the temperature of the residue exiting inline 185 preferably is from 70° C. to 105° C., e.g., from 70° C. to 100°C. or from 75° C. to 95° C. The temperature of the second distillateexiting in line 184 preferably is from 50° C. to 90° C., e.g., from 55°C. to 85° C. or from 65° C. to 80° C. Ethanol sidestream 186 ispreferably withdrawn at the boiling point of ethanol, about 78° C. atatmospheric pressure.

In some embodiments, a portion of the second residue, sidestream orsecond distillate may be dehydrated to form aliphatic alkenes. In oneembodiment, the 2-butanol in the second residue may be dehydrated to2-butene. In another embodiment, the 2-butanol in the second residuestream may be recovered in a separate system.

In one embodiment, instead of purging the second distillate in line 184or the second residue in line 185, a portion thereof may be fed tovaporizer 108. Heavy ends compounds may be removed in the blowdownstream 110.

The ethanol product, either obtained as the second residue in line 182of FIG. 4 or the sidestream in line 186 FIG. 5, may contain smallconcentrations of water. For some ethanol applications, in particularfor fuel applications, it may be desirable to further reduce the waterconcentration. A portion of either ethanol stream may be fed to a waterseparation unit. Water separation unit may include an adsorption unit,one or more membranes, molecular sieves, extractive distillation units,or a combination thereof. Ethanol sidestream may be withdrawn as a vaporor liquid stream, but it may be more suitable to use a vapor stream.Suitable adsorption units include pressure swing adsorption (PSA) unitsand thermal swing adsorption (TSA) units. A PSA unit may be employed toremove water from the ethanol sidestream. PSA unit is operated at atemperature from 30° C. to 160° C., e.g., from 80° C. to 140° C., and apressure from 0.01 kPa to 550 kPa, e.g., from 1 kPa to 150 kPa. The PSAunit may comprise two to five beds. The resulting dried ethanol productstream preferably has a water concentration that is less than 1 wt. %,e.g., less than 0.5 wt. % or less than 0.1 wt. %.

In some embodiments the desired ethanol product is an anhydrous ethanolthat is suitable for uses as a fuel or as a blend for other fuels, suchas gasoline. Water separation unit as described herein may be suitablefor producing anhydrous ethanol.

The columns shown in FIGS. 1 to 5 may comprise any distillation columncapable of performing the desired separation and/or purification. Eachcolumn preferably comprises a tray column having from 1 to 150 trays,e.g., from 10 to 100 trays, from 20 to 95 trays or from 30 to 75 trays.The trays may be sieve trays, fixed valve trays, movable valve trays, orany other suitable design known in the art. In other embodiments, apacked column may be used. For packed columns, structured packing orrandom packing may be employed. The trays or packing may be arranged inone continuous column or they may be arranged in one or more columns,preferably two or more columns such that the vapor from the firstsection enters the second section while the liquid from the secondsection enters the first section, etc.

The associated condensers and liquid separation vessels that may beemployed with each of the distillation columns may be of anyconventional design and are simplified in the figures. Heat may besupplied to the base of each column or to a circulating bottom streamthrough a heat exchanger or reboiler. Other types of reboilers, such asinternal reboilers, may also be used. The heat that is provided to thereboilers may be derived from any heat generated during the process thatis integrated with the reboilers or from an external source such asanother heat generating chemical process or a boiler. Although onereactor and one flasher are shown in the figures, additional reactors,flashers, condensers, heating elements, and other components may be usedin various embodiments of the present invention. As will be recognizedby those skilled in the art, various condensers, pumps, compressors,reboilers, drums, valves, connectors, separation vessels, etc., normallyemployed in carrying out chemical processes may also be combined andemployed in the processes of the present invention.

The temperatures and pressures employed in the columns may vary. As apractical matter, pressures from 10 kPa to 3000 kPa will generally beemployed in these zones although in some embodiments subatmosphericpressures or superatmospheric pressures may be employed. Temperatureswithin the various zones will normally range between the boiling pointsof the composition removed as the distillate and the composition removedas the residue. As will be recognized by those skilled in the art, thetemperature at a given location in an operating distillation column isdependent on the composition of the material at that location and thepressure of column. In addition, feed rates may vary depending on thesize of the production process and, if described, may be genericallyreferred to in terms of feed weight ratios.

The ethanol product produced by the process of the present invention maybe an industrial grade ethanol comprising from 75 to 96 wt. % ethanol,e.g., from 80 to 96 wt. % or from 85 to 96 wt. % ethanol, based on thetotal weight of the ethanol product. Exemplary finished ethanolcompositional ranges are provided below in Table 12.

TABLE 12 FINISHED ETHANOL COMPOSITIONS Conc. Conc. Conc. Component (wt.%) (wt. %) (wt. %) Ethanol 75 to 96 80 to 96 85 to 96 Water <12 1 to 9 3to 8 Acetic Acid <1 <0.1 <0.01 Ethyl Acetate <2 <0.5 <0.05 Acetal <0.05 <0.01  <0.005 Acetone <0.05  <0.01  <0.005 Isopropanol <0.5 <0.1 <0.05n-propanol <0.5 <0.1 <0.05

The finished ethanol composition of the present invention preferablycontains very low amounts, e.g., less than 0.5 wt. %, of other alcohols,such as methanol, butanol, isobutanol, isoamyl alcohol and other C₄-C₂₀alcohols. In one embodiment, the amount of isopropanol in the finishedethanol composition is from 80 to 1,000 wppm, e.g., from 95 to 1,000wppm, from 100 to 700 wppm, or from 150 to 500 wppm. In one embodiment,the finished ethanol composition is substantially free of acetaldehyde,optionally comprising less than 8 wppm acetaldehyde, e.g., less than 5wppm or less than 1 wppm.

In some embodiments, when further water separation is used, the ethanolproduct may be withdrawn as a stream from the water separation unit asdiscussed above. In such embodiments, the ethanol concentration of theethanol product may be higher than indicated in Table 12, and preferablyis greater than 97 wt. % ethanol, e.g., greater than 98 wt. % or greaterthan 99.5 wt. %. The ethanol product in this aspect preferably comprisesless than 3 wt. % water, e.g., less than 2 wt. % or less than 0.5 wt. %.

The finished ethanol composition produced by the embodiments of thepresent invention may be used in a variety of applications includingapplications as fuels, solvents, chemical feedstocks, pharmaceuticalproducts, cleansers, sanitizers, hydrogenation transport or consumption.In fuel applications, the finished ethanol composition may be blendedwith gasoline for motor vehicles such as automobiles, boats and smallpiston engine aircraft. In non-fuel applications, the finished ethanolcomposition may be used as a solvent for toiletry and cosmeticpreparations, detergents, disinfectants, coatings, inks, andpharmaceuticals. The finished ethanol composition may also be used as aprocessing solvent in manufacturing processes for medicinal products,food preparations, dyes, photochemicals and latex processing.

The finished ethanol composition may also be used as a chemicalfeedstock to make other chemicals such as vinegar, ethyl acrylate, ethylacetate, ethylene, glycol ethers, ethylamines, aldehydes, and higheralcohols, especially butanol. In the production of ethyl acetate, thefinished ethanol composition may be esterified with acetic acid. Inanother application, the finished ethanol composition may be dehydratedto produce ethylene. Any known dehydration catalyst can be employed todehydrate ethanol, such as those described in copending U.S. Pub. Nos.2010/0030002 and 2010/0030001, the entireties of which is incorporatedherein by reference. A zeolite catalyst, for example, may be employed asthe dehydration catalyst. Preferably, the zeolite has a pore diameter ofat least 0.6 nm, and preferred zeolites include dehydration catalystsselected from the group consisting of mordenites, ZSM-5, a zeolite X anda zeolite Y. Zeolite X is described, for example, in U.S. Pat. No.2,882,244 and zeolite Yin U.S. Pat. No. 3,130,007, the entireties ofwhich are hereby incorporated herein by reference.

In order that the invention disclosed herein may be more efficientlyunderstood, examples are provided below. It should be understood thatthis example is for illustrative purposes only and is not to beconstrued as limiting the invention in any manner.

EXAMPLES Example 1

A stacked bed reactor was loaded with 100 μl of a catalyst comprising 2wt. % of 25 mol. % platinum and 75 mol. % tin on a high silica zeolite(HSZ™—Tosoh Products) support in a first bed. The stacked bed reactoralso contained a second bed comprising 50 μl of a catalyst comprising 65wt. % copper and 25 wt. % zinc on alumina. A reactant stream comprising70 wt. % acetic acid and 30 wt. % ethyl acetate was fed to the reactor,along with hydrogen, at a GHSV of 1620 hr⁻¹.

Example 2

A stacked bed reactor was loaded with 100 μl of a catalyst comprising 2wt. % of 25 mol. % platinum and 75 mol. % tin on a silica-aluminasupport in a first bed. The stacked bed reactor also contained a secondbed comprising 50 μl of a catalyst comprising 65 wt. % copper and 25 wt.% zinc on alumina. A reactant stream comprising 70 wt. % acetic acid and30 wt. % ethyl acetate was fed to the reactor, along with hydrogen, at aGHSV of 1620 hr⁻¹.

A feed comprising 70 wt. % acetic acid and 30 wt. % ethyl acetate wasfed to reactors of Examples 1 and 2. The acetic acid and ethyl acetateconversions and ethanol and ethyl acetate selectivities are shown inTable 13. The values were measured at 20 hours time on stream and 60hours.

TABLE 13 Example 1 Example 2 TOS (Hours) 20 60 20 60 Acetic AcidConversion (%) 90 70 83 99 Ethanol Selectivity (%) 45 38 40 59 EthylAcetate Selectivity (%) 57 63 50 42

Example 3

A stacked bed reactor was loaded with 100 μl of a catalyst comprising 1wt. % platinum and 1.2 wt. % tin silica support modified with 6 wt. %calcium metasilicate in a first bed. The stacked bed reactor alsocontained a second bed comprising 50 μl of a catalyst comprising 65 wt.% copper and 25 wt. % zinc on alumina. A reactant stream comprising 70wt. % acetic acid and 30 wt. % ethyl acetate was fed to the reactor,along with hydrogen, at a GHSV of 1620 hr⁻¹.

Example 4

A stacked bed reactor was loaded with 100 μl of a catalyst comprising 1wt. % platinum and palladium, 0.1 wt. % cesium, 1.2 wt. % tin on asilica support modified with 14 wt. % of WO₃ in a first bed. The stackedbed reactor also contained a second bed comprising 50 μl of a catalystcomprising 65 wt. % copper and 25 wt. % zinc on alumina. A reactantstream comprising 70 wt. % acetic acid and 30 wt. % ethyl acetate wasfed to the reactor, along with hydrogen, at a GHSV of 1620 hr⁻¹.

A feed comprising 70 wt. % acetic acid and 30 wt. % ethyl acetate wasfed to reactors of Examples 3 and 4. The acetic acid and ethyl acetateconversions and ethanol and ethyl acetate selectivities are shown inTable 14. The values were measured at 20 hours time on stream and 60hours.

TABLE 14 Example 3 Example 4 TOS (Hours) 20 60 20 60 Acetic AcidConversion (%) 90 83 99 99 Ethanol Selectivity (%) 78 82 75 78 EthylAcetate Selectivity (%) 22 18 22 22

Example 5

A stacked bed reactor was loaded with 230 μl of a catalyst comprising 2wt. % of 25 mol. % platinum and 75 mol. % tin on a high silica zeolite(HSZ™—Tosoh Products) support in a first bed. The stacked bed reactoralso contained a second bed comprising 100 μl of a catalyst comprising65 wt. % copper and 25 wt. % zinc on alumina. A reactant streamcomprising essentially pure acetic acid, e.g. greater than 99 wt. %acetic acid, was fed to the reactor, along with hydrogen, at a GHSV of736 hr⁻¹.

Comparative Example A

This examples is similar to Example 5, except only the first catalystfrom the first bed is used. There is no second catalyst.

Example 6

A stacked bed reactor was loaded with 230 μl of a catalyst comprising 2wt. % of 25 mol. % platinum and 75 mol. % tin on a silica-aluminasupport in a first bed. The stacked bed reactor also contained a secondbed comprising 100 μl of a catalyst comprising 65 wt. % copper and 25wt. % zinc on alumina. A reactant stream comprising essentially pureacetic acid, e.g. greater than 99 wt. % acetic acid, was fed to thereactor, along with hydrogen, at a GHSV of 736 hr⁻¹.

Comparative Example B

Similar to Example 6, except only the first catalyst from the first bedis used. There is no second catalyst.

A feed comprising essentially pure acetic acid, e.g. greater than 99 wt.% acetic acid, was fed to reactors of Examples 5 and 6, and ComparativeExamples A and B. The acetic acid and ethyl acetate conversions andethanol and ethyl acetate selectivities are shown in Table 15. Thevalues were measured at 20 hours time on stream and 60 hours.

TABLE 15 Example 5 Comp. A Example 6 Comp. B TOS (Hours) 20 60 20 60 3060 20 60 Acetic Acid 99 99 60 80 99 99 78 83 Conversion (%) Ethanol 8581 18 25 95 95 20 30 Selectivity (%) Ethyl Acetate 5 5 80 75 5 5 76 70Selectivity (%) Methyl Acetate 8.5 10.5 1 2 0.5 1 1 1 Selectivity (%)

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to thoseof skill in the art. In view of the foregoing discussion, relevantknowledge in the art and references discussed above in connection withthe Background and Detailed Description, the disclosures of which areall incorporated herein by reference. In addition, it should beunderstood that aspects of the invention and portions of variousembodiments and various features recited herein and/or in the appendedclaims may be combined or interchanged either in whole or in part. Inthe foregoing descriptions of the various embodiments, those embodimentswhich refer to another embodiment may be appropriately combined withother embodiments as will be appreciated by one of skill in the art.Furthermore, those of ordinary skill in the art will appreciate that theforegoing description is by way of example only, and is not intended tolimit the invention.

We claim:
 1. A process for producing ethanol, comprising the steps of:introducing a feed stream comprising from 5 to 40 wt. % ethyl acetateand from 60 to 95 wt. % acetic acid, and hydrogen into a stacked bedreactor that comprises a first bed and a second bed to produce a crudeethanol product, wherein the first bed comprises a first catalystcomprising platinum and tin on a first support and the second bedcomprises a second catalyst comprising copper or an oxide thereof on asecond support; and recovering ethanol from the crude ethanol product inone or more columns.
 2. The process of claim 1, wherein the feed streamcomprises from 10 to 30 wt. % ethyl acetate and from 70 to 90 wt. %acetic acid.
 3. The process of claim 1, wherein ethyl acetate conversionin the stacked bed reactor is greater than 0%.
 4. The process of claim1, wherein acetic acid conversion in the stacked bed reactor is greaterthan 60%.
 5. The process of claim 1, wherein ethanol selectivity in thestacked bed reactor is greater than selectivity to ethyl acetate.
 6. Theprocess of claim 1, wherein ethanol selectivity is greater than 80%. 7.The process of claim 1, wherein methyl acetate selectivity is less than5%.
 8. The process of claim 1, wherein the ethyl acetate concentrationof the feed is greater than the concentration of ethyl acetate in thecrude ethanol product.
 9. The process of claim 1, wherein the firstsupport is selected from the group consisting of silica, silica/alumina,calcium metasilicate, pyrogenic silica, high purity silica, carbon,activated carbon, alumina, titiana, zirconia, graphite, zeolites, andmixtures thereof.
 10. The process of claim 9, wherein the first supportfurther comprises one or more support modifiers.
 11. The process ofclaim 10, wherein the support modifier is selected from the groupconsisting of (i) alkaline earth metal oxides, (ii) alkali metal oxides,(iii) alkaline earth metal metasilicates, (iv) alkali metalmetasilicates, (v) Group IIB metal oxides, (vi) Group IIB metalmetasilicates, (vii) Group IIIB metal oxides, (viii) Group IIIB metalmetasilicates, and mixtures thereof.
 12. The process of claim 10,wherein the support modifier is selected from the group consisting ofTiO₂, ZrO₂, Nb₂O₅, Ta₂O₅, Al₂O₃, B₂O₃, P₂O₅, Sb₂O₃, WO₃, MoO₃, Fe₂O₃,Cr₂O₃, V₂O₅, MnO₂, CuO, Co₂O₃, and Bi₂O₃.
 13. The process of claim 1,wherein the second catalyst further comprises zinc, aluminum, cobalt, oroxides thereof.
 14. The process of claim 1, wherein the second supportis selected from the group consisting of silica/alumina, alumina,titiana, zeolites, and mixtures thereof.
 15. The process of claim 1,wherein the first support and second support each comprise alumina. 16.The process of claim 1, wherein the first catalyst further comprises oneor more additional metals selected from the group consisting ofpalladium, cesium, and cobalt.
 17. The process of claim 1, wherein thesecond catalyst further comprises one or more additional second metalsselected from the group consisting of cobalt, rhodium, or iridium. 18.The process of claim 1, wherein the reaction in the stacked bed reactoris performed in a vapor phase at a temperature from 125° C. to 350° C.,a pressure of 10 kPa to 3000 kPa, and a hydrogen to acetic acid moleratio of greater than 4:1.
 19. The process of claim 1, wherein the firstbed has a volume that is larger than the second bed.
 20. The process ofclaim 1, further comprising gasifying a carbonaceous material to producethe feed stream, wherein the carbonaceous material is selected from thegroup consisting of oil, coal, natural gas and biomass.
 21. A processfor producing ethanol, comprising the steps of: introducing hydrogen anda feed stream comprising from 5 to 40 wt. % ethyl acetate and 60 to 95wt. % acetic acid into a stacked bed reactor that comprises a first bedand a second bed to produce a crude ethanol product, wherein the firstbed comprises a first catalyst comprising platinum and tin on a firstsupport comprising a support modifier selected from the group consistingof WO₃, MoO₃, Fe₂O₃, Cr₂O₃, Nb₂O₅, V₂O₅, MnO₂, CuO, Co₂O₃, and Bi₂O₃,and the second bed comprises a second catalyst comprising copper or anoxide thereof on a second support; and recovering ethanol from the crudeethanol product in one or more columns.
 22. The process of claim 21,wherein the feed stream comprises 30 wt. % ethyl acetate and 70 wt. %acetic acid.
 23. The process of claim 21, wherein ethyl acetateconversion in the stacked bed reactor is greater than 0% and acetic acidconversion in the stacked bed reactor is greater than 60%.
 24. Theprocess of claim 21, wherein ethanol selectivity in the stacked bedreactor is greater than the selectivity to ethyl acetate.
 25. Theprocess of claim 21, wherein ethanol selectivity is greater than 80%.26. A process for producing ethanol, comprising the steps of:introducing hydrogen and a feed stream comprising from 5 to 40 wt. %ethyl acetate and from 60 to 95 wt. % acetic acid into a stacked bedreactor that comprises a first bed and a second bed to produce a crudeethanol product, wherein the first bed comprises a first catalystcomprising platinum and tin on a first support, and the second bedcomprises a second catalyst comprising copper or an oxide thereof on asecond support, and wherein the first support and second support eachcomprise alumina; and recovering ethanol from the crude ethanol productin one or more columns.
 27. The process of claim 26, wherein the feedstream comprises from 10 to 30 wt. % ethyl acetate and from 70 to 90 wt.% acetic acid.
 28. The process of claim 26, wherein ethyl acetateconversion in the stacked bed reactor is greater than 0%.
 29. Theprocess of claim 26, wherein acetic acid conversion in the stacked bedreactor is greater than 60%, and wherein ethanol selectivity in thestacked bed reactor is greater than selectivity to ethyl acetate. 30.The process of claim 26, wherein ethanol selectivity is greater than80%.
 31. A process for producing ethanol, comprising the steps of:introducing hydrogen and a feed stream comprising from 5 to 40 wt. %ethyl acetate and from 60 to 95 wt. % acetic acid into a stacked bedreactor that comprises a first bed and a second bed to produce a crudeethanol product, wherein the first bed has a bed volume that is largerthan the second bed, wherein the first bed comprises a first catalyst,and the second bed comprises a second catalyst that is different thanthe first catalyst; and recovering ethanol from the crude ethanolproduct in one or more columns.
 32. The process of claim 31, whereinacetic acid conversion in the first bed is greater than 97%.
 33. Theprocess of claim 31, wherein the bed volume of the first bed is at leasttwice as large as the second bed.
 34. The process of claim 31, whereinacetic acid concentration fed to the second bed is less than 3 wt. %.